USArray Imaging of Continental Crust in the Conterminous United States

NASA Astrophysics Data System (ADS)

Ma, Xiaofei; Lowry, Anthony R.

2017-12-01

The thickness and bulk composition of continental crust provide important constraints on the evolution and dynamics of continents. Crustal mineralogy and thickness both may influence gravity anomalies, topographic elevation, and lithospheric strength, but prior to the inception of EarthScope's USArray, seismic measurements of crustal thickness and properties useful for inferring lithology are sparse. Here we improve upon a previously published methodology for joint inversion of Bouguer gravity anomalies and seismic receiver functions by using parameter space stacking of cross correlations of modeled synthetic and observed receiver functions instead of standard H-κ amplitude stacking. The new method is applied to estimation of thickness and bulk seismic velocity ratio, vP/vS, of continental crust in the conterminous United States using USArray and other broadband network data. Crustal thickness variations are reasonably consistent with those found in other studies and show interesting relationships to the history of North American continental formation. Seismic velocity ratios derived in this study are more robust than in other analyses and hint at large-scale variations in composition of continental crust. To interpret the results, we model the pressure-/temperature-dependent thermodynamics of mineral formation for various crustal chemistries, with and without volatile constituents. Our results suggest that hydration lowers bulk crustal vP/vS and density and releases heat in the shallow crust but absorbs heat in the lowermost crust (where plagioclase breaks down to pyroxene and garnet resulting in higher seismic velocity). Hence, vP/vS variations may provide a useful proxy for hydration state in the crust.

Seismicity of the rocky mountains and Rio Grande Rift from the EarthScope Transportable Array and CREST temporary seismic networks, 2008-2010

NASA Astrophysics Data System (ADS)

Nakai, J. S.; Sheehan, A. F.; Bilek, S. L.

2017-03-01

We developed a catalog of small magnitude (ML -0.1 to 4.7) seismicity across Colorado and New Mexico from the EarthScope USArray Transportable Array and CREST (Colorado Rocky Mountains Experiment and Seismic Transects) seismic networks from 2008 to 2010 to characterize active deformation in the Rio Grande Rift. We recorded over 900 earthquakes in the Rio Grande Rift region, not including induced earthquakes and mine blasts, and find that the rift is actively deforming both broadly and in distinct regions. Seismic events that are likely induced, mostly in the Raton Basin, make up 66% of the catalog (1837 earthquakes). Neogene faults in the northern rift in north central Colorado are seismically active in the North Park Basin and northwestern Colorado. The central rift from the San Luis Basin (southern Colorado) to south of the Socorro Magma Body is the most seismically active rift region, and seismicity delineates the deformation in the Colorado Plateau transition zone, which is spatially correlated with volcanic vents, dikes, and faults within the western Jemez Lineament. The eastern Jemez Lineament is nearly aseismic and surrounded by a halo of seismicity culminating in boundaries defined by recent moderate (Mw 3.9 and Mw 3.3) earthquakes. The southern rift is characterized by diffuse seismicity in Texas and Mexico. This study provides an updated seismic catalog built with uniformity in seismometer coverage and low epicentral uncertainties ( 2 km) that allows for regional evaluation of seismicity. During this time period, clusters of seismicity and moderate magnitude earthquakes characterize deformation in a low-strain rate extensional environment.

Providing Web Interfaces to the NSF EarthScope USArray Transportable Array

NASA Astrophysics Data System (ADS)

Vernon, Frank; Newman, Robert; Lindquist, Kent

2010-05-01

Since April 2004 the EarthScope USArray seismic network has grown to over 850 broadband stations that stream multi-channel data in near real-time to the Array Network Facility in San Diego. Providing secure, yet open, access to real-time and archived data for a broad range of audiences is best served by a series of platform agnostic low-latency web-based applications. We present a framework of tools that mediate between the world wide web and Boulder Real Time Technologies Antelope Environmental Monitoring System data acquisition and archival software. These tools provide comprehensive information to audiences ranging from network operators and geoscience researchers, to funding agencies and the general public. This ranges from network-wide to station-specific metadata, state-of-health metrics, event detection rates, archival data and dynamic report generation over a station's two year life span. Leveraging open source web-site development frameworks for both the server side (Perl, Python and PHP) and client-side (Flickr, Google Maps/Earth and jQuery) facilitates the development of a robust extensible architecture that can be tailored on a per-user basis, with rapid prototyping and development that adheres to web-standards. Typical seismic data warehouses allow online users to query and download data collected from regional networks, without the scientist directly visually assessing data coverage and/or quality. Using a suite of web-based protocols, we have recently developed an online seismic waveform interface that directly queries and displays data from a relational database through a web-browser. Using the Python interface to Datascope and the Python-based Twisted network package on the server side, and the jQuery Javascript framework on the client side to send and receive asynchronous waveform queries, we display broadband seismic data using the HTML Canvas element that is globally accessible by anyone using a modern web-browser. We are currently creating additional interface tools to create a rich-client interface for accessing and displaying seismic data that can be deployed to any system running the Antelope Real Time System. The software is freely available from the Antelope contributed code Git repository (http://www.antelopeusersgroup.org).

USArray Siting Outreach: Telling the EarthScope Story

NASA Astrophysics Data System (ADS)

Dorr, P. M.; Taber, J. J.; McQuillan, P.; Busby, R. W.; Woodward, R.

2013-12-01

USArray has engaged in a variety of activities that involve students in and inform the general public about EarthScope. Examples include the highly successful Transportable Array Student Siting Program that employed students and faculty from colleges and universities in the identification of sites for future Transportable Array stations in their region, and a range of informal education and media opportunities where information about EarthScope and its discoveries are shared with educators and the public. During the course of eight summers, more than 135 students from about 55 institutions conducted site reconnaissance for nearly 1375 sites from the West Coast to the East Coast, and from the Gulf of Mexico to the Great Lakes and southern Canada. While telling the EarthScope story, students who participated in the program increased their professional skills and deepened their personal growth. Other students had opportunities to engage in EarthScope-related research as part of the Research Experiences for Undergraduates program. Several EarthScope-focused outreach products for the public and educational audiences have been developed including Ground Motion Visualizations, EarthScope-centric and regional content sets for the IRIS Active Earth Monitor (AEM), and animations of earth processes. A kiosk loan program has helped to broadly disseminate the AEM displays. There have also been articles published in university, local and regional newspapers; stories appearing in national and international print and broadcast media; and documentaries produced by some of the world's most respected scientific and educational production companies that have included a segment about EarthScope and the Transportable Array. Over the next five years, USArray will be deploying and operating Transportable Array stations in Alaska and western Canada. This challenging environment will offer new opportunities to connect with communities throughout the region including native populations.

Data Latency Characteristics Observed Through Diverse Communication Links by the EarthScope USArray Transportable Array

NASA Astrophysics Data System (ADS)

Vernon, F. L.; Eakins, J. A.; Busby, R.

2008-12-01

The USArray Transportable Array has deployed over 600 stations in aggregate over the past four years. All stations communicate in near-real time using ip protocols over a variety of communication links including satellite, cell phone, and DSL. Several different communication providers have been used for each type of communication links. In addition, data are being acquired from several regional networks either directly from a data server or after passing through the IRIS DMC BUD system. We will present results about the latency of data arriving at the UCSD Array Network Facility where the real time data are acquired. Under normal operating conditions the median data latency is several seconds. We will also examine the data return rates through the near-real time systems. In addition we will examine the statistics of over 36,000 events which have automatic event locations and associations. We evaluate the timeliness of these results in the context of seismic early warning systems.

Seismic velocity structure of the crust and shallow mantle of the Central and Eastern United States by seismic surface wave imaging

USGS Publications Warehouse

Pollitz, Fred; Mooney, Walter D.

2016-01-01

Seismic surface waves from the Transportable Array of EarthScope's USArray are used to estimate phase velocity structure of 18 to 125 s Rayleigh waves, then inverted to obtain three-dimensional crust and upper mantle structure of the Central and Eastern United States (CEUS) down to ∼200 km. The obtained lithosphere structure confirms previously imaged CEUS features, e.g., the low seismic-velocity signature of the Cambrian Reelfoot Rift and the very low velocity at >150 km depth below an Eocene volcanic center in northwestern Virginia. New features include high-velocity mantle stretching from the Archean Superior Craton well into the Proterozoic terranes and deep low-velocity zones in central Texas (associated with the late Cretaceous Travis and Uvalde volcanic fields) and beneath the South Georgia Rift (which contains Jurassic basalts). Hot spot tracks may be associated with several imaged low-velocity zones, particularly those close to the former rifted Laurentia margin.

New data products available at the IRIS DMC

NASA Astrophysics Data System (ADS)

Trabant, C. M.; Bahavar, M.; Hutko, A.; Karstens, R.

2010-12-01

The research supported by the raw data from the observatories of NSF's EarthScope project are having tremendous impact on our understanding of the structure and geologic history of North America, how and why earthquakes occur and many other areas of modern geophysics. The IRIS Data Management Center (DMC) is the primary access point for EarthScope/USArray data and has embarked on a new effort to produce higher-level data products beyond raw time series in order to assist the community in extracting the highest value possible from these data. These new products will serve many purposes: stepping-stones for future research projects, data visualizations, research result comparisons and compilation of unique data sets as well as outreach material. To ensure community involvement in the development of new products the requirements and priorities are reviewed and approved by the IRIS Data Products Working Group (DPWG). Many new products are now available at the IRIS DMC. These include two event based products generated in near real time. 1) USArray Ground Motion Visualizations, routinely generated animations showing the both the vertical and horizontal seismic wavefields sweeping across the USArray Transportable Array from earthquakes around the world. 2) Event Plots, a suite of figures automatically generated following all M6.0+ events which include phase aligned record sections, global body wave envelope stacks, regional network vespagrams and source-time functions. 3) Earth Model Collaboration, a new web repository for community-supplied regional and global tomography models with the ability to preview, request and compare models. 4) EARS, the EarthScope Automated Receiver Survey, developed at the University of South Carolina, aims to calculate crustal thickness and bulk crustal properties beneath USArray stations as well as many other broadband stations whose data are archived at the IRIS DMC. 5) Archiving and distribution of Princeton 3D SEM and 1D synthetic seismograms generated for all Global CMT events. 6) Archiving and distribution of GPS displacement time series produced by the Plate Boundary Observatory. Other data products are under consideration and will be moved to the development pipeline once approved by the IRIS DPWG. Feedback on existing products and ideas for new products are welcome at any time.

Delineating Concealed Faults within Cogdell Oil Field via Earthquake Detection

NASA Astrophysics Data System (ADS)

Aiken, C.; Walter, J. I.; Brudzinski, M.; Skoumal, R.; Savvaidis, A.; Frohlich, C.; Borgfeldt, T.; Dotray, P.

2016-12-01

Cogdell oil field, located within the Permian Basin of western Texas, has experienced several earthquakes ranging from magnitude 1.7 to 4.6, most of which were recorded since 2006. Using the Earthscope USArray, Gan and Frohlich [2013] relocated some of these events and found a positive correlation in the timing of increased earthquake activity and increased CO2 injection volume. However, focal depths of these earthquakes are unknown due to 70 km station spacing of the USArray. Accurate focal depths as well as new detections can delineate subsurface faults and establish whether earthquakes are occurring in the shallow sediments or in the deeper basement. To delineate subsurface fault(s) in this region, we first detect earthquakes not currently listed in the USGS catalog by applying continuous waveform-template matching algorithms to multiple seismic data sets. We utilize seismic data spanning the time frame of 2006 to 2016 - which includes data from the U.S. Geological Survey Global Seismographic Network, the USArray, and the Sweetwater, TX broadband and nodal array located 20-40 km away. The catalog of earthquakes enhanced by template matching reveals events that were well recorded by the large-N Sweetwater array, so we are experimenting with strategies for optimizing template matching using different configurations of many stations. Since earthquake activity in the Cogdell oil field is on-going (a magnitude 2.6 occurred on May 29, 2016), a temporary deployment of TexNet seismometers has been planned for the immediate vicinity of Cogdell oil field in August 2016. Results on focal depths and detection of small magnitude events are pending this small local network deployment.

Cyberinfrastructure at IRIS: Challenges and Solutions Providing Integrated Data Access to EarthScope and Other Earth Science Data

NASA Astrophysics Data System (ADS)

Ahern, T. K.; Barga, R.; Casey, R.; Kamb, L.; Parastatidis, S.; Stromme, S.; Weertman, B. T.

2008-12-01

While mature methods of accessing seismic data from the IRIS DMC have existed for decades, the demands for improved interdisciplinary data integration call for new approaches. Talented software teams at the IRIS DMC, UNAVCO and the ICDP in Germany, have been developing web services for all EarthScope data including data from USArray, PBO and SAFOD. These web services are based upon SOAP and WSDL. The EarthScope Data Portal was the first external system to access data holdings from the IRIS DMC using Web Services. EarthScope will also draw more heavily upon products to aid in cross-disciplinary data reuse. A Product Management System called SPADE allows archive of and access to heterogeneous data products, presented as XML documents, at the IRIS DMC. Searchable metadata are extracted from the XML and enable powerful searches for products from EarthScope and other data sources. IRIS is teaming with the External Research Group at Microsoft Research to leverage a powerful Scientific Workflow Engine (Trident) and interact with the web services developed at centers such as IRIS to enable access to data services as well as computational services. We believe that this approach will allow web- based control of workflows and the invocation of computational services that transform data. This capability will greatly improve access to data across scientific disciplines. This presentation will review some of the traditional access tools as well as many of the newer approaches that use web services, scientific workflow to improve interdisciplinary data access.

An Educator's Resource Guide to Earthquakes and Seismology

NASA Astrophysics Data System (ADS)

Johnson, J.; Lahr, J. C.; Butler, R.

2007-12-01

When a major seismic event occurs, millions of people around the world want to understand what happened. This presents a challenge to many classroom science teachers not well versed in Earth science. In response to this challenge, teachers may try surfing the Internet to ferret out the basics. Following popular links can be time consuming and frustrating, so that the best use is not made of this "teachable moment." For isolated rural teachers with limited Internet access, surfing for information may not be a viable option. A partnership between EarthScope/USArray, High Lava Plains Project (Carnegie Institution/Arizona State University, Portland State University, and isolated K-12 schools in rural SE Oregon generated requests for a basic "Teachers Guide to Earthquakes." To bridge the inequalities in information access and varied science background, EarthScope/USArray sponsored the development of a CD that would be a noncommercial repository of Earth and earthquake-related science resources. A subsequent partnership between the University of Portland, IRIS, the USGS, and Portland-area school teachers defined the needs and provided the focus to organize sample video lectures, PowerPoint presentations, new Earth-process animations, and activities on a such a large range of topics that soon the capacity of a DVD was required. Information was culled from oft-referenced sources, always seeking clear descriptions of processes, basic classroom-tested instructional activities, and effective Web sites. Our format uses a master interactive PDF "book" that covers the basics, from the interior of the Earth and plate tectonics to seismic waves, with links to reference folders containing activities, new animations, and video demos. This work-in-progress DVD was initially aimed at middle school Earth-science curriculum, but has application throughout K-16. Strong support has come from university professors wanting an organized collection of seismology resources. The DVD shows how the study of seismology advances our understanding of the Earth and how students and teachers can access seismic data from USArray stations to promote discussion about earthquakes worldwide. Instructions on how to view USArray data, as well as activities using data from EarthScope's vast array of monitoring equipment, are being generated and incorporated as they prove effective.

A Database of Tornado Events as Perceived by the USArray Transportable Array Network

NASA Astrophysics Data System (ADS)

Tytell, J. E.; Vernon, F.; Reyes, J. C.

2015-12-01

Over the course of the deployment of Earthscope's USArray Transportable Array (TA) network there have numerous tornado events that have occurred within the changing footprint of its network. The Array Network Facility based in San Diego, California, has compiled a database of these tornado events based on data provided by the NOAA Storm Prediction Center (SPC). The SPC data itself consists of parameters such as start-end point track data for each event, maximum EF intensities, and maximum track widths. Our database is Antelope driven and combines these data from the SPC with detailed station information from the TA network. We are now able to list all available TA stations during any specific tornado event date and also provide a single calculated "nearest" TA station per individual tornado event. We aim to provide this database as a starting resource for those with an interest in investigating tornado signatures within surface pressure and seismic response data. On a larger scale, the database may be of particular interest to the infrasound research community

GeoFrame Walker Lane: Overview, Rationale, and Objectives

NASA Astrophysics Data System (ADS)

Stockli, D. F.

2006-12-01

GeoFrame is an integrative geologic initiative that takes a multi-dimensional view of the building and modification of the North American continent by systematic integration of geologic and geochronometric investigations and the results from unprecedented geophysical imaging as part of the Earthscope Program. The GeoFrame effort envisions these focus site investigations to entail map-scale arrays of passive source seismic receivers and associated active source seismic studies and complementary geophysics in conjunction with geologic-based synthesis and targeted studies. One of these focus sites is the Walker Lane region in eastern California and western Nevada, situated between the Basin and Range province and the unextended Sierra Nevada block. This GeoFrame focus site workshop is particularly timely given the deployment schedule of the USArray "BigFoot" array. The Walker Lane intraplate deformation zone accommodates nearly ~25% of present-day relative motion between the Pacific and North American plates and might represent an incipient plate boundary. It provides a world-class example of the present modification of continental lithosphere by the process of transcurrent faulting and rifting and offers the opportunity to seamlessly integrate surface geology, structural geology, petrology, geo- and thermochronology, and the history of the continental lithosphere with ongoing processes in the Earth's mantle. It affords opportunities to address a number of questions posed within Earthscope such as: mechanisms of strain transfer, the role of lithospheric rheology in strain localization and seismic response, the nature and timescales of transient fault behavior, and the role of magmas and fluids in deforming lithosphere. Implicit in the design and implementation of Earthscope is the recognition that progress on issues such as these requires an integrative geophysical and geological investigation of the Walker Lane. As such, it will open new avenues of collaboration and identify new research needs and opportunities. We anticipate the integration of results and efforts with ongoing Earthscope projects, such as Sierra Nevada efforts of SNEP as well as the NSF Margins Rupturing of Continental Lithosphere (RCL) initiative in the Gulf of California by continuing the work onshore from the Gulf of California to the north into Nevada.

Deep Seismic Structure of the Texas-Gulf of Mexico Passive Margin

NASA Astrophysics Data System (ADS)

Pulliam, J.; Gurrola, H.

2013-12-01

The Texas-Gulf of Mexico region has witnessed a wide range of tectonic processes, including deformation due to orogeny, continental collision and rifting. Artifacts of these processes are likely to remain at lithospheric depths beneath the region but, until recently, the tools needed to examine structures at mantle depths were not available. With the passage of the EarthScope's USArray stations and the completion of a targeted broadband deployment, new images of the region's lithosphere have emerged. These images reveal lithospheric-scale anomalies that correlate strongly with surface features, such as a large fast anomaly that corresponds to the southern extent of the Laurentia (or 'Great Plains') craton and a large slow anomaly associated with the Southern Oklahoma Aulacogen. Other features that would not have been expected based on surface tectonics include a slow layer that we interpret to be a shear zone at the base of the cratonic root and the transitional continental lithosphere, and a zone that is bounded at its top and bottom by discontinuities and high levels of seismic anisotropy. Additionally a high velocity body underlying the Gulf Coast Plains may mark delaminating lower crust. If true it provides indirect evidence that active rifting best describes the process that led to the opening of the Gulf of Mexico. These new results are based upon the analysis of 326 USArray broadband seismic stations and a 23-station broadband deployment across Texas' passive margin, from Matagorda Island, a barrier island in the Gulf of Mexico, to Johnson City, TX, on the relatively undisturbed Proterozoic crust of central Texas.

Structure and tectonics of the northwestern United States from EarthScope USArray magnetotelluric data

USGS Publications Warehouse

Bedrosian, Paul A.; Feucht, Daniel W.

2014-01-01

The magnetotelluric component of the EarthScope USArray program has covered over 35% of the continental United States. Resistivity tomography models derived from these data image lithospheric structure and provide constraints on the distribution of fluids and melt within the lithosphere. We present a three-dimensional resistivity model of the northwestern United States which provides new insight into the tectonic assembly of western North America from the Archean to present. Comparison with seismic tomography models reveals regions of correlated and anti-correlated resistivity and velocity that help identify thermal and compositional variations within the lithosphere. Recent (Neogene) tectonic features reflected in the model include the subducting Juan de Fuca–Gorda plate which can be traced beneath the forearc to more than 100 km depth, high lithospheric conductivity along the Snake River Plain, and pronounced lower-crustal and upper-mantle conductivity beneath the Basin and Range. The latter is abruptly terminated to the northwest by the Klamath–Blue Mountains Lineament, which we interpret as an important structure during and since the Mesozoic assembly of the region. This boundary is interpreted to separate hot extended lithosphere from colder, less extended lithosphere. The western edge of Proterozoic North America, as indicated by the Cretaceous initial 87Sr/86Sr = 0.706 contour, is clearly reflected in the resistivity model. We further image an Archean crustal block (“Pend Oreille block”) straddling the Washington/Idaho border, which we speculate separated from the Archean Medicine Hat block in the Proterozoic. Finally, in the modern Cascades forearc, the geometry and internal structure of the Eocene Siletz terrane is reflected in the resistivity model. The apparent eastern edge of the Siletz terrane under the Cascades arc suggests that pre-Tertiary rocks fill the Washington and Oregon back-arc.

Visualizing Data from EarthScope's USArray

NASA Astrophysics Data System (ADS)

Woodward, R.; Frassetto, A.; Adinolfi, A.

2012-12-01

The EarthScope USArray program has generated a large volume of data from across the North American continent. The Transportable Array (TA) component of USArray has deployed over 400 seismic stations in a grid with 70 km spacing between stations. The TA has rolled the array across the contiguous US states over a ten-year period, and will have occupied over 1600 distinct sites from the Pacific Ocean to the Atlantic Ocean by the end of 2013. All stations transmit multiple channels of 40 samples per second data continuously, in near real time. Each station records and transmits seismic, barometric pressure, and infrasound data, as well as various state-of-health data streams. All data are immediately open and unrestricted. The TA provides a unique tool for visualizing large-scale seismic wave phenomena. The power of this tool is particularly apparent when displaying simultaneous signals from all stations as a function of time, as well as rendering multiple channels of data from each station. In this situation it is challenging to convey the 3D motion at each station as well as the aggregate 3D motion across the entire set of 400 stations. Creating movies of the data becomes essential to illustrate the time dependence of the observations. Typically the rendering of such movies requires the use of programming language that is suitable for both data analysis and graphics, as it is essential to explore different data pre-processing strategies (often filtering, but also including other pre-processing steps). Different visualization strategies provide a means for dealing with the very large volume of data generated by the TA. Typical data review strategies include a survey mode to scan large volumes of data for signals of interest, or zooming in on fine features using combinations of specialized data processing and frame-by-frame time-steps, or going back and forth between the two modes. The data visualizations are continuously evolving to explore new ideas. The movie-based representations of the data also provide an excellent medium for education and outreach. Complex wave phenomena become immediately visible to both the trained and untrained eye. Yet there are challenges in conveying an understanding of how the output of a single sensor relates to the output of multiple sensors, and how color variations are used to represent at least one of the dimensions. Conventions that are common to a scientific audience may not be familiar to other audiences. We have explored strategies for trying to add a perspective view and a sense of spatial orientation to the visualizations to make them more useful in educational settings. Some of these visualizations are now routinely produced as data products to support research and education. We will provide examples of the visualization results, including movies of seismic surface waves spreading out on the planet and the use of perspective views, cross-sections, contours, and other graphical techniques as a means to gain insight into the data. We will also provide examples of the time and spatial evolution of barometric pressure variations, seismic background noise, and solar irradiance. Examples of data visualizations created for both specialists and non-specialists will be included.

Constraints on the Geometry of the Farallon Slab from the Joint Interpretation of All Available Imaging Results from the Earthscope USArray Deployment in the Lower 48 States

NASA Astrophysics Data System (ADS)

Esker, A.; Pavlis, G. L.

2017-12-01

We assembled all available seismic tomography models distributed through the IRIS DMC and other sources. We combined these images with our own results using 3D plane wave migration of P to S conversion data derived from the USArray data set and other broadband seismic stations in the lower 48 states. All the tomography models were converted into SEGY format and interpolated onto a regular grid in a UTM reference frame. That innovation makes joint interpretation feasible using a seismic interpretation software (Petrel) because we treat both the tomography models and scattered wave image results as if they were 3D seismic reflection data. The careful designed interface of a modern exploration package makes exploring a range of interpretation packages much faster and allowed us to produce a more comprehensive interpretation of all available data. The tomography models are nearly an order of magnitude smoother than the scattered wave images, so we use the tomography models as a cross-validation in interpretation unless the scattered wave images are ambiguous. The focus of this study is testing a conjecture in an earlier paper (Pavlis, 2011) for the presence of a single continuous horizon interpreted as the top of the Farallon Slab. As in the previous paper we constrained the western edge of this surface with the location of Cascadia trench as well as a virtual edge from a back projection of the Mendocino triple junction using Pacific-North America motion over the past 30 Ma. We also simulated crustal multiple effects on the plane wave migration results using crustal geometry estimates produced by the Earthscope Automated Receiver Survey (EARS). This confirmed the scattered wave images were not reliable in the upper mantle at depths shallower than 200 km due to contamination by crustal multiples. Most tomography models show a steep dip in the slab immediately east of the volcanic arc and our surface follows the average geometry defined by a visual comparison of all the models. In eastern Oregon and northern Nevada the tomography models consistently show a general flattening of the slab over the 410 km discontinuity. A consistent horizon is observed in the most recent plane wave imaging and at we use that horizon to define the top of slab there. Our interpretations also confirmed a sharp increase in dip of the slab in eastern Wyoming and Montana.

Llnking the EarthScope Data Virtual Catalog to the GEON Portal

NASA Astrophysics Data System (ADS)

Lin, K.; Memon, A.; Baru, C.

2008-12-01

The EarthScope Data Portal provides a unified, single-point of access to EarthScope data and products from USArray, Plate Boundary Observatory (PBO), and San Andreas Fault Observatory at Depth (SAFOD) experiments. The portal features basic search and data access capabilities to allow users to discover and access EarthScope data using spatial, temporal, and other metadata-based (data type, station specific) search conditions. The portal search module is the user interface implementation of the EarthScope Data Search Web Service. This Web Service acts as a virtual catalog that in turn invokes Web services developed by IRIS (Incorporated Research Institutions for Seismology), UNAVCO (University NAVSTAR Consortium), and GFZ (German Research Center for Geosciences) to search for EarthScope data in the archives at each of these locations. These Web Services provide information about all resources (data) that match the specified search conditions. In this presentation we will describe how the EarthScope Data Search Web service can be integrated into the GEONsearch application in the GEON Portal (see http://portal.geongrid.org). Thus, a search request issued at the GEON Portal will also search the EarthScope virtual catalog thereby providing users seamless access to data in GEON as well as the Earthscope via a common user interface.

Exploring Seismic Noise with the USArray Transportable Array

NASA Astrophysics Data System (ADS)

Woodward, R.; Busby, R. W.; Simpson, D. W.

2009-12-01

The large number of seismic stations that comprise the EarthScope USArray Transportable Array (TA) seismic network provide an unparalleled opportunity for studying how seismic noise evolves with time over a large portion of the North American continent. Power spectra for every station in the TA data are computed automatically, for every hour of every station-day, by the Quality Analysis Control Kit (QUACK) system at the IRIS Data Management Center. The power spectra utilize hour-long data segments, with 50% overlap between segments, providing spectral values in the band between 20 Hz and 172 s. Thus, at any in-band frequency one can construct a continuous two-year time history of seismic noise for every TA station. When the time variation of the power spectra values across the array are rendered as individual movie frames one can examine the evolution of seismic noise across the full spatio-temporal extent of the TA. Overall, the background noise levels (especially at periods below 10 s) are remarkably uniform across the entire array. Numerous expected features are present, including diurnal and annual variations, enhanced noise levels at coastal stations, transients related to large storms, and episodes when the observations of background noise are dominated by earthquake energy. Upgrades to the TA station instrumentation will provide the capability to measure additional physical factors relevant to seismic noise. All TA stations deployed after August 2009 include MEMS barometers that can measure atmospheric pressure from DC to approximately 0.1 Hz. In additional, several stations have been temporarily equipped with infrasound sensors. Previous research has highlighted the direct effect of atmospheric pressure fluctuations on very long period vertical seismometers. The relationship to noise observed on horizontal seismometers is more complex. However, with a large number of uniform installations it may be possible to make further progress. We will present analyses of the spatio-temporal evolution of noise observed on the TA stations and present preliminary results from the barometers and infrasound sensors that have been deployed with TA stations so far. We will discuss opportunities for augmenting TA stations with additional sensors that may further elucidate seismic noise processes.

Induced Seismicity in the Bakken: Much Ado about Almost Nothing

NASA Astrophysics Data System (ADS)

Frohlich, C.; Walter, J. I.; Gale, J.

2014-12-01

This study investigates possible links between seismicity and wastewater injection in the Williston Basin and Bakken Formation in North Dakota and Montana. To identify Bakken earthquakes we analyzed seismic records collected by the EarthScope USArray temporary network of seismograph stations, deployed on a grid with 70-km spacing. During the September 2008 - May 2011 study period we identified only nine earthquakes; of these only three were near injection wells. Thus, possibly triggered earthquakes are rarer near injection wells in the Bakken than in the Barnett Shale of Texas, or in central Oklahoma. The reason why Bakken earthquakes are so scarce is unclear. In many respects the Bakken/Williston region is similar to the Barnett Shale/Fort Worth Basin of Texas. In both regions injection volumes increased significantly in late 2007, and both areas have low levels of natural seismicity. Yet, in Johnson and Tarrant counties in the Barnett, earthquakes near injection wells were numerous; in the Bakken and elsewhere in the Barnett, earthquakes near wells were scarce. An important result of these surveys is that the relationship between seismicity and injection/production activities varies considerably in different geographic areas. In the Bakken and western counties of Texas' Barnett Shale, there is almost no seismic activity near injection wells. In Oklahoma, Arkansas, parts of the Barnett, and near Timpson in east Texas, there are earthquakes associated with high-volume injection wells. In the Eagle Ford of Texas earthquakes are associated primarily with production (not injection). And near Snyder, TX, recent earthquakes are associated with CO2injection. This variability in response to injection complicates efforts to craft uniform policies or regulations to mitigate potential seismic hazards associated with injection practices. At a minimum it suggests that within particular geographic regions it is important to survey the relationship between seismicity and injection before considering possible policy responses or regulations. For these regional surveys, the records collected during the two-year deployment of USArray stations are valuable, although these may need to be augmented by continuing coverage. Figure: Earthquakes, explosions, injection wells, and coal mines in the Bakken (shaded area).

Montana: Filling A Gap In The GeoSwath

NASA Astrophysics Data System (ADS)

Jensen, B.; Keller, G. R.

2010-12-01

The proposed Geoswath transect crosses southern Montana, and the swath of MT stations deployed as part of EarthScope cover all but a small portion of eastern Montana. USArray broadband stations of course cover the entire region. However, modern controlled-source seismic data are very sparse in this large state, and most of it dates from the 1960’s. In this study, we have taken an integrated approach to analyzing lithospheric structure by compiling and analyzing all the public domain geophysical results and data we could locate and combining them with industry seismic reflection data that were released for our study. This information was employed to interpret a suite of filtered regional maps gravity and magnetic data and to construct integrated gravity models of long profiles that reflect crustal structure and deeper features within the upper mantle of the region. Our analysis included previous seismic refraction/reflection results, EarthScope Automated Array receiver functions, new 2D seismic reflection data, seismic tomography, potential field data, and previous geological studies in order to investigate structural and compositional variations within the crust and upper mantle. Our targets included Precambrian structure and tectonics, Sevier and Laramide features, and Late Cenozoic extension. Our main conclusions are: 1) Receiver function and seismic refraction/reflection crustal thickness estimates show a W-E crustal thickening with thicknesses greater than 50 km in the central and eastern Montana; 2) Seismic reflection data reveal Laramide basement-involved structures as far east as central Montana. These structures also show that the western edge of the North American craton was affected by late Mesozoic to Cenozoic deformation and has thus been decratonized; 3) Potential field filtering methods revealed regional trends and tectonic province outlines. The tilt derivative of the reduced-to-pole magnetic data enhances crystalline basement patterns that reflect tectonic province boundary locations. The upward continuation of the complete Bouguer anomaly grid revealed a gravity high in the northeast portion of the region, which is interpreted to be associated with density variations in the upper mantle. This interpretation is consistent with seismic tomography that reveals a “wedge-like” zone fast material beneath the craton in this region.

Remotely Triggered Earthquakes Recorded by EarthScope's Transportable Array and Regional Seismic Networks: A Case Study Of Four Large Earthquakes

NASA Astrophysics Data System (ADS)

Velasco, A. A.; Cerda, I.; Linville, L.; Kilb, D. L.; Pankow, K. L.

2013-05-01

Changes in field stress required to trigger earthquakes have been classified in two basic ways: static and dynamic triggering. Static triggering occurs when an earthquake that releases accumulated strain along a fault stress loads a nearby fault. Dynamic triggering occurs when an earthquake is induced by the passing of seismic waves from a large mainshock located at least two or more fault lengths from the epicenter of the main shock. We investigate details of dynamic triggering using data collected from EarthScope's USArray and regional seismic networks located in the United States. Triggered events are identified using an optimized automated detector based on the ratio of short term to long term average (Antelope software). Following the automated processing, the flagged waveforms are individually analyzed, in both the time and frequency domains, to determine if the increased detection rates correspond to local earthquakes (i.e., potentially remotely triggered aftershocks). Here, we show results using this automated schema applied to data from four large, but characteristically different, earthquakes -- Chile (Mw 8.8 2010), Tokoku-Oki (Mw 9.0 2011), Baja California (Mw 7.2 2010) and Wells Nevada (Mw 6.0 2008). For each of our four mainshocks, the number of detections within the 10 hour time windows span a large range (1 to over 200) and statistically >20% of the waveforms show evidence of anomalous signals following the mainshock. The results will help provide for a better understanding of the physical mechanisms involved in dynamic earthquake triggering and will help identify zones in the continental U.S. that may be more susceptible to dynamic earthquake triggering.

Sensor Emplacement Techniques and Seismic Noise Analysis for USArray Transportable Array Seismic Stations

NASA Astrophysics Data System (ADS)

Frassetto, A.; Busby, R. W.; Hafner, K.; Woodward, R.; Sauter, A.

2013-12-01

In preparation for the upcoming deployment of EarthScope's USArray Transportable Array (TA) in Alaska, the National Science Foundation (NSF) has supported exploratory work on seismic station design, sensor emplacement, and communication concepts appropriate for this challenging high-latitude environment. IRIS has installed several experimental stations to evaluate different sensor emplacement schemes both in Alaska and in the lower-48 of the U.S. The goal of these tests is to maintain or enhance a station's noise performance while minimizing its footprint and the weight of the equipment, materials, and overall expense required for its construction. Motivating this approach are recent developments in posthole broadband seismometer design and the unique conditions for operating in Alaska, where there are few roads, cellular communications are scarce, most areas are only accessible by small plane or helicopter, and permafrost underlies much of the state. We will review the methods used for directly emplacing broadband seismometers in comparison to the current methods used for the lower-48 TA. These new methods primarily focus on using a portable drill to make a bored hole three to five meters, beneath the active layer of the permafrost, or by coring 1-2 meters deep into surface bedrock. Both methods are logistically effective in preliminary trials. Subsequent station performance has been assessed quantitatively using probability density functions summed from power spectral density estimates. These are calculated for the continuous time series of seismic data recorded for each channel of the seismometer. There are five test stations currently operating in Alaska. One was deployed in August 2011 and the remaining four in October 2012. Our results show that the performance of seismometers in Alaska with auger-hole or core-hole installations can sometimes exceed that of the quietest TA stations in the lower-48, particularly horizontal components at long periods. A comparison of the performance of the various installations is discussed.

Upper Mantle Discontinuity Structure Beneath the Western Atlantic Ocean and Eastern North America from SS Precursors

NASA Astrophysics Data System (ADS)

Schmerr, N. C.; Beghein, C.; Kostic, D.; Baldridge, A. M.; West, J. D.; Nittler, L. R.; Bull, A. L.; Montesi, L.; Byrne, P. K.; Hummer, D. R.; Plescia, J. B.; Elkins-Tanton, L. T.; Lekic, V.; Schmidt, B. E.; Elkins, L. J.; Cooper, C. M.; ten Kate, I. L.; Van Hinsbergen, D. J. J.; Parai, R.; Glass, J. B.; Ni, J.; Fuji, N.; McCubbin, F. M.; Michalski, J. R.; Zhao, C.; Arevalo, R. D., Jr.; Koelemeijer, P.; Courtier, A. M.; Dalton, H.; Waszek, L.; Bahamonde, J.; Schmerr, B.; Gilpin, N.; Rosenshein, E.; Mach, K.; Ostrach, L. R.; Caracas, R.; Craddock, R. A.; Moore-Driskell, M. M.; Du Frane, W. L.; Kellogg, L. H.

2015-12-01

Seismic discontinuities within the mantle arise from a wide range of mechanisms, including changes in mineralogy, major element composition, melt content, volatile abundance, anisotropy, or a combination of the above. In particular, the depth and sharpness of upper mantle discontinuities at 410 and 660 km depth are attributed to solid-state phase changes sensitive to both mantle temperature and composition, where regions of thermal heterogeneity produce topography and chemical heterogeneity changes the impedance contrast across the discontinuity. Seismic mapping of this topography and sharpness thus provides constraint on the thermal and compositional state of the mantle. The EarthScope USArray is providing unprecedented access to a wide variety of new regions previously undersampled by the SS precursors. This includes the boundary between the oceanic plate in the western Atlantic Ocean and continental margin of eastern North America. Here we use a seismic array approach to image the depth, sharpness, and topography of the upper mantle discontinuities, as well as other possible upper mantle reflectors beneath this region. This array approach utilizes seismic waves that reflect off the underside of a mantle discontinuity and arrive several hundred seconds prior to the SS seismic phase as precursory energy. In this study, we collected high-quality broadband data SS precursors data from shallow focus (< 30 km deep), mid-Atlantic ridge earthquakes recorded by USArray seismometers in Alaska. We generated 4th root vespagrams to enhance the SS precursors and determine how they sample the mantle. Our data show detection of localized structure on the discontinuity boundaries as well as additional horizons, such as the X-discontinuity and a potential reflection from a discontinuity near the depth of the lithosphere-asthenosphere boundary. These structures are related to the transition from predominantly old ocean lithosphere to underlying continental lithosphere, as while deeper reflectors are associated with the subduction of the ancient Farallon slab. A comparison of the depth of upper mantle discontinuities to changes in seismic velocity and anisotropy will further quantify the relationship to mantle flow, compositional layering, and phases changes.

Visualizing how Seismic Waves Propagate Across Seismic Arrays using the IRIS DMS Ground Motion Visualization (GMV) Products and Codes

NASA Astrophysics Data System (ADS)

Taber, J.; Bahavar, M.; Bravo, T. K.; Butler, R. F.; Kilb, D. L.; Trabant, C.; Woodward, R.; Ammon, C. J.

2011-12-01

Data from dense seismic arrays can be used to visualize the propagation of seismic waves, resulting in animations effective for teaching both general and advanced audiences. One of the first visualizations of this type was developed using Objective C code and EarthScope/USArray data, which was then modified and ported to the Matlab platform and has now been standardized and automated as an IRIS Data Management System (IRIS-DMS) data product. These iterative code developments and improvements were completed by C. Ammon, R. Woodward and M. Bahavar, respectively. Currently, an automated script creates Ground Motion Visualizations (GMVs) for all global earthquakes over magnitude 6 recorded by EarthScope's USArray Transportable Array (USArray TA) network. The USArray TA network is a rolling array of 400 broadband stations deployed on a uniform 70-km grid. These near real-time GMV visualizations are typically available for download within 4 hours or less of their occurrence (see: www.iris.edu/dms/products/usarraygmv/). The IRIS-DMS group has recently added a feature that allows users to highlight key elements within the GMVs, by providing an online tool for creating customized GMVs. This new interface allows users to select the stations, channels, and time window of interest, adjust the mapped areal extent of the view, and specify high and low pass filters. An online tutorial available from the IRIS Education and Public Outreach (IRIS-EPO) website, listed below, steps through a teaching sequence that can be used to explain the basic features of the GMVs. For example, they can be used to demonstrate simple concepts such as relative P, S and surface wave velocities and corresponding wavelengths for middle-school students, or more advanced concepts such as the influence of focal mechanism on waveforms, or how seismic waves converge at an earthquake's antipode. For those who desire a greater level of customization, including the ability to use the GMV framework with data sets not stored within the IRIS-DMS, the Matlab GMV code is now also available from the IRIS-DMS website. These GMV codes have been applied to sac-formatted data from the Quake Catcher Network (QCN). Through a collaboration between NSF-funded programs and projects (e.g., IRIS and QCN) we are striving to make these codes user friendly enough to be routinely incorporated in undergraduate and graduate seismology classes. In this way, we will help provide a research tool for students to explore never-looked-at-before data, similar to actual seismology research. As technology is advancing quickly, we now have more data than seismologists can easily examine. Given this, we anticipate students using our codes can perform a 'citizen scientist' role in that they can help us identify key signals within the unexamined vast data streams we are acquiring.

Converting Advances in Seismology into Earthquake Science

NASA Astrophysics Data System (ADS)

Hauksson, Egill; Shearer, Peter; Vidale, John

2004-01-01

Federal and state agencies and university groups all operate seismic networks in California. The U.S. Geological Survey (USGS) operates seismic networks in California in cooperation with the California Institute of Technology (Caltech) in southern California, and the University of California (UC) at Berkeley in northern California. The California Geological Survey (CGS) and the USGS National Strong Motion Program (NSMP) operate dial-out strong motion instruments in the state, primarily to capture data from large earthquakes for earthquake engineering and, more recently, emergency response. The California Governor's Office of Emergency Services (OES) provides leadership for the most recent project, the California Integrated Seismic Network (CISN), to integrate all of the California efforts, and to take advantage of the emergency response capabilities of the seismic networks. The core members of the CISN are Caltech, UC Berkeley, CGS, USGS Menlo Park, and USGS Pasadena (http://www.cisn.org). New seismic instrumentation is in place across southern California, and significant progress has been made in improving instrumentation in northern California. Since 2001, these new field instrumentation efforts, data sharing, and software development for real-time reporting and archiving have been coordinated through the California Integrated Seismic Network (CISN). The CISN is also the California region of the Advanced National Seismic Network (ANSS). In addition, EarthScope deployments of USArray that will begin in early 2004 in California are coordinated with the CISN. The southern and northern California earthquake data centers (SCEDC and NCEDC) have new capabilities that enable seismologists to obtain large volumes of data with only modest effort.

Berkeley Seismological Laboratory Seismic Moment Tensor Report for the August 6, 2007 M3.9 Seismic event in central Utah

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ford, S; Dreger, D; Hellweg, P

2007-08-08

We have performed a complete moment tensor analysis of the seismic event, which occurred on Monday August 6, 2007 at 08:48:40 UTC 21 km from Mt.Pleasant, Utah. In our analysis we utilized complete three-component seismic records recorded by the USArray, University of Utah, and EarthScope seismic arrays. The seismic waveform data was integrated to displacement and filtered between 0.02 to 0.10 Hz following instrument removal. We used the Song et al. (1996) velocity model to compute Green's functions used in the moment tensor inversion. A map of the stations we used and the location of the event is shown inmore » Figure 1. In our moment tensor analysis we assumed a shallow source depth of 1 km consistent with the shallow depth reported for this event. As shown in Figure 2 the results point to a source mechanism with negligible double-couple radiation and is composed of dominant CLVD and implosive isotropic components. The total scalar seismic moment is 2.12e22 dyne cm corresponding to a moment magnitude (Mw) of 4.2. The long-period records are very well matched by the model (Figure 2) with a variance reduction of 73.4%. An all dilational (down) first motion radiation pattern is predicted by the moment tensor solution, and observations of first motions are in agreement.« less

Unraveling earthquake stresses: Insights from dynamically triggered and induced earthquakes

NASA Astrophysics Data System (ADS)

Velasco, A. A.; Alfaro-Diaz, R. A.

2017-12-01

Induced seismicity, earthquakes caused by anthropogenic activity, has more than doubled in the last several years resulting from practices related to oil and gas production. Furthermore, large earthquakes have been shown to promote the triggering of other events within two fault lengths (static triggering), due to static stresses caused by physical movement along the fault, and also remotely from the passage of seismic waves (dynamic triggering). Thus, in order to understand the mechanisms for earthquake failure, we investigate regions where natural, induced, and dynamically triggered events occur, and specifically target Oklahoma. We first analyze data from EarthScope's USArray Transportable Array (TA) and local seismic networks implementing an optimized (STA/LTA) detector in order to develop local detection and earthquake catalogs. After we identify triggered events through statistical analysis, and perform a stress analysis to gain insight on the stress-states leading to triggered earthquake failure. We use our observations to determine the role of different transient stresses in contributing to natural and induced seismicity by comparing these stresses to regional stress orientation. We also delineate critically stressed regions of triggered seismicity that may indicate areas susceptible to earthquake hazards associated with sustained fluid injection in provinces of induced seismicity. Anthropogenic injection and extraction activity can alter the stress state and fluid flow within production basins. By analyzing the stress release of these ancient faults caused by dynamic stresses, we may be able to determine if fluids are solely responsible for increased seismic activity in induced regions.

The Earthscope USArray Array Network Facility (ANF): Evolution of Data Acquisition, Processing, and Storage Systems

NASA Astrophysics Data System (ADS)

Davis, G. A.; Battistuz, B.; Foley, S.; Vernon, F. L.; Eakins, J. A.

2009-12-01

Since April 2004 the Earthscope USArray Transportable Array (TA) network has grown to over 400 broadband seismic stations that stream multi-channel data in near real-time to the Array Network Facility in San Diego. In total, over 1.7 terabytes per year of 24-bit, 40 samples-per-second seismic and state of health data is recorded from the stations. The ANF provides analysts access to real-time and archived data, as well as state-of-health data, metadata, and interactive tools for station engineers and the public via a website. Additional processing and recovery of missing data from on-site recorders (balers) at the stations is performed before the final data is transmitted to the IRIS Data Management Center (DMC). Assembly of the final data set requires additional storage and processing capabilities to combine the real-time data with baler data. The infrastructure supporting these diverse computational and storage needs currently consists of twelve virtualized Sun Solaris Zones executing on nine physical server systems. The servers are protected against failure by redundant power, storage, and networking connections. Storage needs are provided by a hybrid iSCSI and Fiber Channel Storage Area Network (SAN) with access to over 40 terabytes of RAID 5 and 6 storage. Processing tasks are assigned to systems based on parallelization and floating-point calculation needs. On-site buffering at the data-loggers provide protection in case of short-term network or hardware problems, while backup acquisition systems at the San Diego Supercomputer Center and the DMC protect against catastrophic failure of the primary site. Configuration management and monitoring of these systems is accomplished with open-source (Cfengine, Nagios, Solaris Community Software) and commercial tools (Intermapper). In the evolution from a single server to multiple virtualized server instances, Sun Cluster software was evaluated and found to be unstable in our environment. Shared filesystem architectures using PxFS and QFS were found to be incompatible with our software architecture, so sharing of data between systems is accomplished via traditional NFS. Linux was found to be limited in terms of deployment flexibility and consistency between versions. Despite the experimentation with various technologies, our current virtualized architecture is stable to the point of an average daily real time data return rate of 92.34% over the entire lifetime of the project to date.

The Maupin, Oregon Earthquake Swarm

NASA Astrophysics Data System (ADS)

Braunmiller, J.; Williams, M.; Trehu, A. M.; Nabelek, J.

2008-12-01

The area near Maupin, Oregon has experienced over 300 earthquakes since December 2006. The events, located by the Pacific Northwest Seismic Network (PNSN), occurred ~10 km SE of the town in central Oregon and ~50 km E-SE of Mount Hood. The temporal event pattern and lack of a distinct main shock are characteristic of an earthquake swarm with the event-size distribution indicating a low b-value similar to other non-volcanic swarms. Locations show a NW-SE trending, ~4x3 km cluster at apparent depths of 12-24 km. The largest events (Mw=3.8 and 3.9) on March 1, 2007 and July 14, 2008 occurred more than one year apart; 11 other events had a magnitude of 3 or greater. The larger events were felt locally. During the first 14 months EarthScope USArray seismic stations surrounded the swarm, providing a unique high-quality dataset. Waveform similarity at the closest USArray site G06A indicates hypocenters are much tighter than suggested by the PNSN distribution. Moment tensor inversion reveals nearly identical double- couple strike-slip mechanisms on a plane striking ~15° NW for the three largest 2007 events and the July 2008 event. The April 2008 Mw=3.3 event is rotated ~10° clockwise consistent with slight changes of G06A three-component waveforms relative to the other events. Preferred centroid depths are in the 15-20 km range. Historically, seismicity in the Pacific Northwest east of the Cascades is characterized by sporadic bursts of clustered seismicity with occasional M=6 earthquakes. The largest instrumentally recorded earthquake near Maupin (Mw=4.6) occurred 1976. An earlier swarm was observed 1987, but since then only ~2 events/yr occurred until the current swarm. In spite of recurrent seismicity, exposed surface rocks near Maupin are undeformed lava flows of the Columbia River Basalt Group and older John Day volcanics. The geologic map of Oregon shows a NW-trending dip slip fault near the epicenter area, inconsistent with moment tensor solutions. The cause for the swarm is currently unknown with hypotheses ranging from magmatic or fluid motion in the crust to tectonic activity along a weakly coupled microplate boundary.

Teacher Directed Design: Content Knowledge, Pedagogy and Assessment under the Nevada K-12 Real-Time Seismic Network

NASA Astrophysics Data System (ADS)

Cantrell, P.; Ewing-Taylor, J.; Crippen, K. J.; Smith, K. D.; Snelson, C. M.

2004-12-01

Education professionals and seismologists under the emerging SUN (Shaking Up Nevada) program are leveraging the existing infrastructure of the real-time Nevada K-12 Seismic Network to provide a unique inquiry based science experience for teachers. The concept and effort are driven by teacher needs and emphasize rigorous content knowledge acquisition coupled with the translation of that knowledge into an integrated seismology based earth sciences curriculum development process. We are developing a pedagogical framework, graduate level coursework, and materials to initiate the SUN model for teacher professional development in an effort to integrate the research benefits of real-time seismic data with science education needs in Nevada. A component of SUN is to evaluate teacher acquisition of qualified seismological and earth science information and pedagogy both in workshops and in the classroom and to assess the impact on student achievement. SUN's mission is to positively impact earth science education practices. With the upcoming EarthScope initiative, the program is timely and will incorporate EarthScope real-time seismic data (USArray) and educational materials in graduate course materials and teacher development programs. A number of schools in Nevada are contributing real-time data from both inexpensive and high-quality seismographs that are integrated with Nevada regional seismic network operations as well as the IRIS DMC. A powerful and unique component of the Nevada technology model is that schools can receive "stable" continuous live data feeds from 100's seismograph stations in Nevada, California and world (including live data from Earthworm systems and the IRIS DMC BUD - Buffer of Uniform Data). Students and teachers see their own networked seismograph station within a global context, as participants in regional and global monitoring. The robust real-time Internet communications protocols invoked in the Nevada network provide for local data acquisition, remote multi-channel data access, local time-series data management, interactive multi-window waveform display and time-series analysis with centralized meta-data control. Formally integrating educational seismology into the K-12 science curriculum with an overall "positive" impact to science education practices necessarily requires a collaborative effort between professional educators and seismologists yet driven exclusively by teacher needs.

EarthScope Education and Outreach: Accomplishments and Emerging Opportunities

NASA Astrophysics Data System (ADS)

Robinson, S.; Ellins, K. K.; Semken, S. C.; Arrowsmith, R.

2014-12-01

EarthScope's Education and Outreach (E&O) program aims to increase public awareness of Earth science and enhance geoscience education at the K-12 and college level. The program is distinctive among major geoscience programs in two ways. First, planning for education and public engagement occurred in tandem with planning for the science mission. Second, the NSF EarthScope program includes funding support for education and outreach. In this presentation, we highlight key examples of the program's accomplishments and identify emerging E&O opportunities. E&O efforts have been collaboratively led by the EarthScope National Office (ESNO), IRIS, UNAVCO, the EarthScope Education and Outreach Subcommittee (EEOSC) and PI-driven EarthScope projects. Efforts by the EEOSC, guided by an EarthScope Education and Outreach Implementation Plan that is periodically updated, focus EarthScope E&O. EarthScope demonstrated early success in engaging undergraduate students (and teachers) in its mission through their involvement in siting USArray across the contiguous U.S. Funded E&O programs such as TOTLE, Illinois EarthScope, CEETEP (for K-12), InTeGrate and GETSI (for undergraduates) foster use of freely available EarthScope data and research findings. The Next Generation Science Standards, which stress science and engineering practices, offer an opportunity for alignment with existing EarthScope K-12 educational resources, and the EEOSC recommends focusing efforts on this task. The EEOSC recognizes the rapidly growing use of mobile smart devices by the public and in formal classrooms, which bring new opportunities to connect with the public and students. This will capitalize on EarthScope's already prominent social media presence, an effort that developed to accomplish one of the primary goals of the EarthScope E&O Implementation Plan to "Create a high-profile public identity for EarthScope" and to "Promote science literacy and understanding of EarthScope among all audiences through informal education venues" Leveraging ESNO, IRIS, and UNAVCO resources has exceeded the capabilities of any single entity, thereby amplifying the impact of EarthScope's education and outreach effort.

Differences in the Upper Mantle Structure between 'Hot' and 'Cold' Areas in North America based on USArray Seismic Data along California - Virginia Profile

NASA Astrophysics Data System (ADS)

Dec, M.; Sroda, P.; Tesauro, M.; Kaban, M. K.; Perchuc, E.

2013-12-01

Nowadays, United States is an area extensively studied by seismic research due to the fact that the EarthScope USArray project provides an unique opportunity to verify previous seismological models and improve our understanding of the upper mantle structure. The data from this experiment are fundamental to study the upper mantle structure because they allow us to present much more detailed analysis. In this study we use the data recorded by the Transportable Array of the USArray and data from the ISC bulletin. We refer also to data from longitudinal Early Rise project while analysing New Madrid Seismic Zone. We use the travel time data from the earthquakes recorded at a distance up to 3500 km in order to image the upper mantle down to about 600 km depth. We present P- and S-wave velocity models for the tectonically stable central part of US and for the active western part. The 1D models are constructed based on the forward modelling of traveltimes from the events located along the California - Virginia profile, for e.g. in California, Colorado or Virginia. This provides a possibility to update the previous MP-1 model (Malinowski et al., 2010). The models were corrected for the crustal effect using the crustal model of Tesauro et al. (2013). All the models have been verified by synthetic seismograms calculated using the reflectivity method. The models show significant differences in the first-arrivals observed at the 800-1800 km epicentral distance range. In the Western, tectonically active region, the 300-km discontinuity is observed. It is interpreted based on the refracted phases with the apparent velocity of 8.9-9.0 km/s and clearly observed reflections. In this area, a low-velocity zone at the bottom of the upper mantle significantly deepens the 410-km discontinuity. The stable North American Craton is characterized by blurred arrivals from the 300-km discontinuity. These 1D models of the upper mantle structure in North America served as a starting point for calculation of a 2D model along the profile using forward and inversion approach. We distinguish three parts in our profile: western - tectonically active, central cratonic - stable one and eastern - tectonically active. The New Madrid Seismic Zone is characterized by an anomalous structure in the lower lithosphere at the offset ~2500km. Very interesting part of the studied area is the marginal part of North American Craton, which separates two tectonically different areas. The seismic P- and S-wave velocity models were inverted for temperature using different mantle composition and anelasticity models. The modelling results are in agreement with those obtained for the strength and the elastic thickness of the lithosphere.

EMSCOPE - Electromagnetic Component of EarthScope Backbone and Transportable Array Experiments 2006-2008

NASA Astrophysics Data System (ADS)

Egbert, G.; Evans, R.; Ingate, S.; Livelybrooks, D.; Mickus, K.; Park, S.; Schultz, A.; Unsworth, M.; Wannamaker, P.

2007-12-01

USArray (http://www.iris.edu/USArray) in conjunction with EMSOC (Electromagnetic Studies of the Continents) (http://emsoc.ucr.edu/emsoc) is installing magnetotelluric (MT) stations as part of Earthscope. The MT component of Earthscope consists of permanent (Backbone) and transportable long period stations to record naturally occurring, time varying electric and magnetic fields to produce a regional lithospheric/asthensospheric electrical conductivity map of the United States. The recent arrival of 28 long period MT instruments allows for the final installation of the Backbone stations throughout the US and yearly transportable array studies. The Backbone MT survey consists of 7 stations spaced throughout the continental US with preliminary installation at Soap Creek, Oregon; Parkfield, California; Braden, Missouri and Socorro, New Mexico.Siting and permitting are underway or completed at stations in eastern Montana, northern Wisconsin and Virginia. These stations will be recording for at least five years to determine electrical conductivities at depths that extend into the mantle transition zone. The first transportable array experiment was performed in the summer and fall of 2006 in central and eastern Oregon (Oregon Pilot Project) using equipment loaned from EMSOC. Thirty-one long period MT stations were recorded with 14 to 21 day occupations. Preliminary 3D inverse models indicate several lithospheric electrical conductivity anomalies including a linear zone marked by low-high conductivity transition along the Klamath-Blue Mountain Lineament associated with a linear trend of gravity minima. High electrical conductivity values occur in the upper crust under the accreted terrains in the Blue Mountains region. The second transportable array experiment was performed in the summer and fall of 2007 and completes coverage of the Oregon, Washington, and western Idaho, targeting the Cascadia subduction zone, Precambrian boundaries, and sub-basalt lithologies. The 2008 transportable MT experiment will focus on the Snake River Plain and the Yellowstone Hot Spot. The disposition of future USArray magnetotelluric geotransects will be the subject of an upcoming NSF-supported planning workshop. Time series are available now from the IRIS data center (www.iris.edu/data), and magnetotelluric transfer functions will soon be available.

The role of Facilities in Engaging and Informing the Public of EarthScope Science

NASA Astrophysics Data System (ADS)

Charlevoix, D. J.; Taber, J. J.; Berg, M.; Dorr, P. M.; McQuillan, P.; Olds, S. E.

2013-12-01

The IRIS and UNAVCO facilities play an important role in support of EarthScope through joint and independent education and outreach activities. These activities are focused on providing data and data products to a wide range of audiences, disseminating EarthScope science results through formal and informal venues, and informing the public of the broader impacts of EarthScope. The facilities are particularly well-suited for sustained engagement of multiple audiences over the decade-long course of EarthScope. One such example of a long-term effort was the Transportable Array student siting program, where over an 8 year period, students from about 55 institutions across the US and Canada conducted site reconnaissance and talked to landowners about EarthScope. Another activity focused on students was the development of a student intern program to support field engineering efforts during the construction of the Plate Boundary Observatory. Other ongoing activities include developing and maintaining relationships with media representatives and annual training of National Parks staff throughout the western U.S. The UNAVCO-IRIS partnership has been particularly valuable for EarthScope-related activities, where UNAVCO and IRIS work closely with the EarthScope National Office (ESNO) to bring EarthScope science to national, regional and local audiences within the EarthScope footprint. Collaborations have ranged across each group's products and services, including: EarthScope-focused teacher workshops, participation in EarthScope interpretive workshops for informal educators (led by ESNO), development of content for the IRIS Active Earth Monitor, preparing PBO-, USArray- and EarthScope-focused materials on topics such as Episodic Tremor and Slip for wider distribution through print, web, and mobile information technologies, and organizing research experiences for undergraduates on EarthScope-related topics. Other collaborations have focused on social media, and the development and dissemination of materials for the scientifically interested public at science and technology centers. The presentation will also share techniques used and future plans for evaluation of the public impact of EarthScope.

Filling the monitoring gaps across the US Arctic by permanently adopting USArray stations

NASA Astrophysics Data System (ADS)

Buurman, H.; West, M. E.

2017-12-01

The USArray project represents a truly unique opportunity to fundamentally change geophysical monitoring in the US Arctic. The addition of more than 200 stations capable of recording seismic, infrasound, ground temperature and meteorologic data has brought a diverse group of organizations to the table, fostering new connections and collaborations between scientists whose paths otherwise would not cross. With the array slated for removal beginning in 2019, there is a window of opportunity to advocate for permanently retaining a subset of the USArray stations. The Alaska Earthquake Center has drafted a plan to permanently adopt a subset of the USArray stations and maintain them as part of the seismic network in Alaska. The expanded seismic network would substantially improve on the Alaska Earthquake Center's ongoing mission to advance Alaska's resilience to earthquake hazards. By continuing to provide public climate and infrasound data, the Alaska Earthquake Center would also fill important gaps in the weather, wildfire and climate research monitoring networks across Alaska. The many challenges in adopting USArray stations include choosing which stations to retain, upgrading the power systems to have 24/7 data transmission through the long Alaskan winter months, and lowering the costs of continuous telemetry.

Studies of infrasound propagation using the USArray seismic network (Invited)

NASA Astrophysics Data System (ADS)

Hedlin, M. A.; Degroot-Hedlin, C. D.; Walker, K. T.

2010-12-01

Although there are currently ~ 100 infrasound arrays worldwide, more than ever before, the station density is still insufficient to provide validation for detailed propagation modeling. Much structure in the atmosphere is short-lived and occurs at spatial scales much smaller than the average distance between infrasound stations. Relatively large infrasound signals can be observed on seismic channels due to coupling at the Earth's surface. Recent research, using data from the 70-km spaced 400-station USArray and other seismic network deployments, has shown the value of dense seismic network data for filling in the gaps between infrasound arrays. The dense sampling of the infrasound wavefield has allowed us to observe complete travel-time branches of infrasound signals and shed more light on the nature of infrasound propagation. We present early results from our studies of impulsive atmospheric sources, such as series of UTTR rocket motor detonations in Utah. The Utah blasts have been well recorded by USArray seismic stations and infrasound arrays in Nevada and Washington State. Recordings of seismic signals from a series of six events in 2007 are used to pinpoint the shot times to < 1 second. Variations in the acoustic branches and signal arrival times at the arrays are used to probe variations in atmospheric structure. Although we currently use coupled signals we anticipate studying dense acoustic network recordings as the USArray is currently being upgraded with infrasound microphones. These new sensors will allow us to make semi-continental scale network recordings of infrasound signals free of concerns about how the signals observed on seismic channels were modified when being coupled to seismic.

Lithospheric strucutre and relationship to seismicity beneath the Southeastern US using reciever functions

NASA Astrophysics Data System (ADS)

Cunningham, E.; Lekic, V.

2017-12-01

Despite being on a passive margin for millions of years, the Southeastern United States (SEUS) contains numerous seismogenic zones with the ability to produce damaging earthquakes. However, mechanisms controlling these intraplate earthquakes are poorly understood. Recently, Biryol et al. 2016 use P-wave tomography suggest that upper mantle structures beneath the SEUS correlate with areas of seismicity and seismic quiescence. Specifically, thick and fast velocity lithosphere beneath North Carolina is stable and indicative of areas of low seismicity. In contrast, thin and slow velocity lithosphere is weak, and the transition between the strong and weak lithosphere may be correlated with seismogenic zones found in the SEUS. (eg. Eastern Tennessee seismic zone and the Central Virginia seismic zone) Therefore, I systematically map the heterogeneity of the mantle lithosphere using converted seismic waves and quantify the spatial correlation between seismicity and lithospheric structure. The extensive network of seismometers that makes up the Earthscope USArray combined with the numerous seismic deployments in the Southeastern United States allows for unprecedented opportunity to map changes in lithospheric structure across seismogenic zones and seismic quiescent regions. To do so, I will use both P-to-s and S-to-p receiver functions (RFS). Since RFs are sensitive to seismic wavespeeds and density discontinuities with depth, they particularly useful for studying lithospheric structure. Ps receiver functions contain high frequency information allowing for high resolution, but can become contaminated by large sediment signals; therefore, I removed sediment multiples and correct for time delays of later phases using the method of Yu et. al 2015 which will allow us to see later arriving phases associated with lithospheric discontinuities. S-to-p receiver functions are not contaminated by shallow layers, making them ideal to study deep lithospheric structures but they can suffer from low signal-to-noise levels. I compensate for this difficulty by using high quality deployments and stacking these data at common conversion points to increase lateral resolution.

Posthole Sensor Performance in the USArray Transportable Array - Results from Testing and Initial Deployments in Alaska and Canada

NASA Astrophysics Data System (ADS)

Frassetto, A.; Busby, R. W.; Hafner, K.; Sauter, A.; Woodward, R.

2014-12-01

To prepare for the deployment of EarthScope's USArray Transportable Array (TA) in Alaska and adjacent Canada over the next several years, IRIS has evaluated different strategies for emplacing posthole seismometers. The goal of this work has been to maintain or enhance a TA station's noise performance while reducing the weight and logistical considerations required for its installation. Motivating this research are developments in posthole broadband seismometer design and the unique conditions for operating in this region, where many potential sites are located on frost-fractured outcrops or underlain by permafrost, in either case only accessible by helicopter. Current emplacement methods use a portable rig to auger or hammer-drill a hole 2.5-5 meters deep, in unconsolidated materials and permafrost, or by diamond bit coring 1-3 meters into rock. These emplacements are used at new TA installations and upgrades to existing AK network stations, and we compare their performance to the lower-48 TA vault installations. Through July 2014 there are eight TA and six upgraded AK stations operating under USArray; including five since at least October 2012, providing a detailed record of seasonal and/or site-specific behavior. We also discuss testing of different downhole configurations for 13 stations deployed at Piñon Flat Observatory in California since April 2014. Station performance is presented and compared using probability density functions summed from hourly power spectral density calculations. These are computed for the continuous time series of seismic data recorded on each seismic channel. Our results show that the noise performance of seismometers in Alaska with cased- or core- hole installations sometimes exceeds that of the quietest TA stations in the lower-48, particularly for the horizontal channels at long periods. We analyze and discuss the performance of example stations, comparing to other nearby seismometers. We also examine the performance of AK stations before and after they have been converted from surface vault to posthole configuration. At Piñon Flat, different methods for packing the seismometer and clamping its cables within cased holes has guided development of field procedure. The new posthole emplacements generally improve upon the mean performance of the lower-48 TA vaults.

Revisiting Notable Earthquakes and Seismic Patterns of the Past Decade in Alaska

NASA Astrophysics Data System (ADS)

Ruppert, N. A.; Macpherson, K. A.; Holtkamp, S. G.

2015-12-01

Alaska, the most seismically active region of the United States, has produced five earthquakes with magnitudes greater than seven since 2005. The 2007 M7.2 and 2013 M7.0 Andreanof Islands earthquakes were representative of the most common source of significant seismic activity in the region, the Alaska-Aleutian megathrust. The 2013 M7.5 Craig earthquake, a strike-slip event on the Queen-Charlotte fault, occurred along the transform plate boundary in southeast Alaska. The largest earthquake of the past decade, the 2014 M7.9 Little Sitkin event in the western Aleutians, occurred at an intermediate depth and ruptured along a gently dipping fault through nearly the entire thickness of the subducted Pacific plate. Along with these major earthquakes, the Alaska Earthquake Center reported over 250,000 seismic events in the state over the last decade, and its earthquake catalog surpassed 500,000 events in mid-2015. Improvements in monitoring networks and processing techniques allowed an unprecedented glimpse into earthquake patterns in Alaska. Some notable recent earthquake sequences include the 2008 Kasatochi eruption, the 2006-2008 M6+ crustal earthquakes in the central and western Aleutians, the 2010 and 2015 Bering Sea earthquakes, the 2014 Noatak swarm, and the 2014 Minto earthquake sequence. In 2013, the Earthscope USArray project made its way into Alaska. There are now almost 40 new Transportable Array stations in Alaska along with over 20 upgraded sites. This project is changing the earthquake-monitoring scene in Alaska, lowering magnitude of completeness across large, newly instrumented parts of the state.

Sensor Emplacement Techniques and Seismic Noise Analysis for USArray Transportable Array Seismic Stations

NASA Astrophysics Data System (ADS)

Busby, Robert; Frassetto, Andy; Hafner, Katrin; Woodward, Robert; Sauter, Allan

2013-04-01

In preparation for deployment of EarthScope's USArray Transportable Array (TA) in Alaska beginning in 2014, the National Science Foundation (NSF) is supporting exploratory work on seismic station design, sensor emplacement and communication concepts appropriate for the challenging high-latitude environment that is proposed for deployment. IRIS has installed several experimental stations to evaluate different sensor emplacement schemes both in Alaska and the lower-48 U.S. The goal of these tests is to maintain or enhance a station's noise performance while minimizing its footprint and the equipment, materials, and overall expense required for its construction. Motivating this approach are recent developments in posthole broadband seismometer design and the unique conditions for operating in Alaska, where there are few roads, cellular communications are scarce, most areas are only accessible by small plane or helicopter, and permafrost underlies much of the northern tundra. In this study we review our methods used for directly emplacing of broadband seismometers in comparison to the current methods used to deploy TA stations. These primarily focus on using an auger to drill three to five meters, beneath the active layer of the permafrost, or coring directly into surface bedrock to one meter depth using a portable drill. Both methods have proven logistically effective in trials. Subsequent station performance can be quantitatively assessed using probability density functions summed from power spectral density estimates. These are calculated for the continuous time series of seismic data recorded for each channel of the seismometer. There are five test stations currently operating in Alaska. One was deployed in August 2011 and the remaining four in October 2012. Our results show that the performance of seismometers in Alaska with auger-hole or core-hole installations equals or exceeds that of the quietest TA stations in the lower-48, particularly at long periods, and in exceptional cases approaches the performance of the GSN low noise model. The station at Poker Flat Research Range, Alaska co-locates a sensor in a 5 meter deep auger hole with a 2 meter deep TA tank installation typical of the lower-48. The augered seismometer is currently over 20 dB quieter at periods over 40 seconds than the TA tank installation. Similar performance has been observed at other TA stations, which also compare favorably to co-located permanent stations.

Interactive Geophysical Mapping on the Web

NASA Astrophysics Data System (ADS)

Meertens, C.; Hamburger, M.; Estey, L.; Weingroff, M.; Deardorff, R.; Holt, W.

2002-12-01

We have developed a set of interactive, web-based map utilities that make geophysical results accessible to a large number and variety of users. These tools provide access to pre-determined map regions via a simple Html/JavaScript interface or to user-selectable areas using a Java interface to a Generic Mapping Tools (GMT) engine. Users can access a variety of maps, satellite images, and geophysical data at a range of spatial scales for the earth and other planets of the solar system. Developed initially by UNAVCO for study of global-scale geodynamic processes, users can choose from a variety of base maps (satellite mosaics, global topography, geoid, sea-floor age, strain rate and seismic hazard maps, and others) and can then add a number of geographic and geophysical overlays for example coastlines, political boundaries, rivers and lakes, NEIC earthquake and volcano locations, stress axes, and observed and model plate motion and deformation velocity vectors representing a compilation of 2933 geodetic measurements from around the world. The software design is flexible allowing for construction of special editions for different target audiences. Custom maps been implemented for UNAVCO as the "Jules Verne Voyager" and "Voyager Junior", for the International Lithosphere Project's "Global Strain Rate Map", and for EarthScope Education and Outreach as "EarthScope Voyager Jr.". For the later, a number of EarthScope-specific features have been added, including locations of proposed USArray (seismic), Plate Boundary Observatory (geodetic), and San Andreas Fault Observatory at Depth sites plus detailed maps and geographically referenced examples of EarthScope-related scientific investigations. In addition, we are developing a website that incorporates background materials and curricular activities that encourage users to explore Earth processes. A cluster of map processing computers and nearly a terabyte of disk storage has been assembled to power the generation of interactive maps and provide space for a very large collection of map data. A portal to these map tools can be found at: http://jules.unavco.ucar.edu.

Detection of Induced Seismicity Due to Oil and Gas Extraction in the Northern Gulf of Mexico, USA

NASA Astrophysics Data System (ADS)

Fadugba, O. I.; Ebel, J.

2014-12-01

Drilling operations and extraction of oil and gas (O&G) may lead to subsurface slumping or compression of sediments due to reduced vertical principal stress which may lead to small earthquakes at the drilling site. O&G extraction is common in the northern Gulf of Mexico (NGM) and only thirty-five earthquakes of magnitudes between 2.3 and 6.0 have been recorded in the area from 1974 to the present. The purpose of this research is to detect more earthquakes using stacks of seismic data from the EarthScope Transportable USArray (TA) from 2011 to 2013, and determine the spatiotemporal relationship between the detected earthquakes and O&G extraction. TA waveform records were retrieved from IRIS database and a narrow bandpass filter of 1 - 2 Hz was applied to remove background and high frequency noises and focus on the low energy part of the signal. The seismic record at all stations was plotted vertically with respect to distance from the Gulf. An Automatic Gain Control (AGC) using Root Mean Square was applied to boost the signals at farther stations. More than 1500 events have been detected, including teleseisms and local blasts from the area, especially from the three Walter Minerals coal mines in Alabama. No offshore earthquakes have been detected in the data, although data processing is still ongoing. Therefore, any earthquake activity, if present, associated with the offshore oil and gas production must be at a magnitude below the detection threshold of the algorithm.

Analyzing the Possibility of Dynamic Earthquake Triggering in Socorro, New Mexico

NASA Astrophysics Data System (ADS)

Morton, E.; Bilek, S. L.

2011-12-01

The release of energy during an earthquake changes the stress state and seismicity both locally and remotely. Far-field stress changes can lead to triggered earthquakes coinciding with the arrival of the surface waves. This dynamic triggering is found to occur in a variety of tectonic settings, but in particular magmatic regions. Here we test whether the Socorro Magma Body region in central New Mexico hosts triggered seismicity. Preliminary inspection of continuous network data in central New Mexico suggested a local triggered event with the passage of surface waves from an MW 6.9 event in 2009. For a more comprehensive view, we examine data from 379 earthquakes MW ≥ 6.0 between January 15, 2008 to March 13, 2010 recorded on the EarthScope USArray Transportable Network stations located within New Mexico and providing more dense coverage for better detectability. Waveforms from twenty EarthScope stations were windowed around the time of the large event, high-pass filtered at 5 Hz to remove low frequency signals and analyzed to detect high frequency triggered local earthquakes. For each possible trigger detected, waveforms from nine short-period stations in the Socorro Seismic Network were added to aid in locating the events. In the time period analyzed, twelve triggered events were detected. Only one of these events, on August 30, 2009, corresponded to the arrival of surface waves, occurring about a minute after their arrival. The majority of the triggered events occur well after the arrival of the surface waves, indicating that they are either independent of the main shock or the result of delayed dynamic triggering. Delayed dynamic triggering can occur hours or days after the passage of surface waves, and are marked by an increase in seismicity relative to background. Only one of the events, on September 18, 2009, occurred within the Socorro Magma Body area. The rest of these events occur spread throughout New Mexico. The widely spread distribution of possibly triggered events and the low ratio of triggers to main shocks indicates that the rifted magmatic region above the Socorro Magma Body is not particularly susceptible to dynamic triggering from remote main shocks. The lack of direct correspondence to a seismic phase can mean that the detected events may be independent (not triggered events), or the result of delayed dynamic triggering. A comparison to randomly chosen waveforms within the time period as background will reveal if the possible events are a result of delayed dynamic triggering or part of the background.

Existing Instrumentation and Scientific Drivers for a Subduction Zone Observatory in Latin America

NASA Astrophysics Data System (ADS)

Frassetto, A.; Woodward, R.; Detrick, R. S.

2015-12-01

The subduction zones along the western shore of the Americas provide numerous societally relevant scientific questions that have yet to be fully explored and would make an excellent target for a comprehensive, integrated Subduction Zone Observatory (SZO). Further, recent discussions in Latin America indicate that there are a large number of existing stations that could serve as a backbone for an SZO. Such preexisting geophysical infrastructure commonly plays a vital role in new science initiatives, from small PI-led experiments to the establishment of the USArray Transportable Array, Reference Network, Cascadia Amphibious Array, and the redeployment of EarthScope Transportable Array stations to Alaska. Creating an SZO along the western coast of the Americas could strongly leverage the portfolio of existing seismic and geodetic stations across regions of interest. In this presentation, we will discuss the concept and experience of leveraging existing infrastructure in major new observational programs, outline the state of geophysical networks in the Americas (emphasizing current seismic networks but also looking back on historical temporary deployments), and provide an overview of potential scientific targets in the Americas that encompass a sampling of recently produced research results and datasets. Additionally, we will reflect on strategies for establishing meaningful collaborations across Latin America, an aspect that will be critical to the international partnerships, and associated capacity building, needed for a successful SZO initiative.

Research and Teaching About the Deep Earth

NASA Astrophysics Data System (ADS)

Williams, Michael L.; Mogk, David W.; McDaris, John

2010-08-01

Understanding the Deep Earth: Slabs, Drips, Plumes and More; Virtual Workshop, 17-19 February and 24-26 February 2010; Images and models of active faults, subducting plates, mantle drips, and rising plumes are spurring new excitement about deep-Earth processes and connections between Earth's internal systems and plate tectonics. The new results and the steady progress of Earthscope's USArray across the country are also providing a special opportunity to reach students and the general public. The pace of discoveries about the deep Earth is accelerating due to advances in experimental, modeling, and sensing technologies; new data processing capabilities; and installation of new networks, especially the EarthScope facility. EarthScope is an interdisciplinary program that combines geology and geophysics to study the structure and evolution of the North American continent. To explore the current state of deep-Earth science and ways in which it can be brought into the undergraduate classroom, 40 professors attended a virtual workshop given by On the Cutting Edge, a program that strives to improve undergraduate geoscience education through an integrated cooperative series of workshops and Web-based resources. The 6-day two-part workshop consisted of plenary talks, large and small group discussions, and development and review of new classroom and laboratory activities.

High seismic velocity (7.x) lower crustal layers in cratonic North America: a view from xenoliths and EarthScope seismic data

NASA Astrophysics Data System (ADS)

Mahan, K. H.; Barnhart, K. R.; Schulte-Pelkum, V.; Blackburn, T.; Bowring, S. A.; Dudas, F. O.

2010-12-01

Continental crust worldwide has local areas with a lowermost layer characterized by unusually high seismic P velocities of over 7 km/s. The presence (or absence) of these high-velocity layers, as well as their thickness, composition and degree of heterogeneity, can have a profound influence on the rheological properties and behavior of the lower crust. These data also provide fundamental information about lithospheric growth and destruction processes. In North America, high-velocity layers have been inferred for portions of a significant number of seismic refraction lines, as well as from surface wave and receiver function studies. However, the 2-D and localized nature of most existing studies leave many open questions regarding the full spatial extent of these layers (e.g. correlations with Archean vs Proterozoic terranes, collisional or accretionary boundaries, rift zones or plume tracks, etc.). EarthScope’s USArray provides an exceptional opportunity to improve our knowledge of the distribution of 7.x layers in North America. Similarly, xenoliths provide a complimentary opportunity to investigate compositional, geochronological, and petrophysical characteristics of the lower crust in selected areas. In Montana and Wyoming, where seismic experiments reveal an anomalously thick (up to 25 km) 7.x layer, our studies emphasize the heterogeneity in modes of formation, physical properties, and age of the lower crust. We highlight an example from xenoliths exhumed by Eocene minettes from the Great Falls Tectonic Zone in central Montana. The suite includes mafic garnet granulites, mafic eclogite, and felsic granulites with peak pressures of 0.8-1.5+ GPa, consistent with derivation from depths of 28-55+ km. Multiple samples preserve evidence for prograde burial and some are polymetamorphic. One sample (likely a restite from melted supracrustal material) contains evidence for an early mid-crustal metamorphic event followed by an increase in pressure from <0.8 to >1.0 GPa. Another sample records prograde breakdown of plagioclase and peak eclogite-facies conditions, followed by retrograde decompression and reentry into the plagioclase stability field. Prograde burial may represent thickening during collision across the Great Falls Tectonic Zone. Calculated seismic velocities are also heterogeneous with data from samples within the seismically defined 7.x layer ranging from 6.5 to 7.5 km/s. Zircon, monazite, titanite, and rutile U-(Th)-Pb data indicate igneous, metamorphic and/or fluid flow events at 2.7-2.6 Ga, 2.1 Ga, 1.8-1.7 Ga, and 1.3 Ga. Collectively, the data point to incremental assembly of the 7.x layer in Montana from Archean to Mesoproterozoic time. Other potentially similar studies across the continent, especially when combined with seismic techniques employing EarthScope’s USArray and other experiments, allow significant improvements in the development of models for the formation, evolution and present day structure of the North American lithosphere.

Voyager Interactive Web Interface to EarthScope

NASA Astrophysics Data System (ADS)

Eriksson, S. C.; Meertens, C. M.; Estey, L.; Weingroff, M.; Hamburger, M. W.; Holt, W. E.; Richard, G. A.

2004-12-01

Visualization of data is essential in helping scientists and students develop a conceptual understanding of relationships among many complex types of data and keep track of large amounts of information. Developed initially by UNAVCO for study of global-scale geodynamic processes, the Voyager map visualization tools have evolved into interactive, web-based map utilities that can make scientific results accessible to a large number and variety of educators and students as well as the originally targeted scientists. A portal to these map tools can be found at: http://jules.unavco.org. The Voyager tools provide on-line interactive data visualization through pre-determined map regions via a simple HTML/JavaScript interface (for large numbers of students using the tools simultaneously) or through student-selectable areas using a Java interface to a Generic Mapping Tools (GMT) engine. Students can access a variety of maps, satellite images, and geophysical data at a range of spatial scales for the earth and other planets of the solar system. Students can also choose from a variety of base maps (satellite mosaics, global topography, geoid, sea-floor age, strain rate and seismic hazard maps, and others) and can then add a number of geographic and geophysical overlays, for example coastlines, political boundaries, rivers and lakes, earthquake and volcano locations, stress axes, and observed and model plate motion, as well as deformation velocity vectors representing a compilation of over 5000 geodetic measurements from around the world. The related educational website, "Exploring our Dynamic Planet", (http://www.dpc.ucar.edu/VoyagerJr/jvvjrtool.html) incorporates background materials and curricular activities that encourage students to explore Earth processes. One of the present curricular modules is designed for high school students or introductory-level undergraduate non-science majors. The purpose of the module is for students to examine real data to investigate how plate tectonic processes are reflected in observed geophysical phenomena. Constructing maps by controlling map parameters and answering open-ended questions which describe, compare relationships, and work with both observed and model data, promote conceptual understanding of plate tectonics and related processes. The goals of curricular development emphasize inquiry, development of critical thinking skills, and student-centered interests. Custom editions of the map utility have been made as the "Jules Verne Voyager" and "Voyager Junior", for the International Lithosphere Project's "Global Strain Rate Map", and for EarthScope Education and Outreach as "EarthScope Voyager Jr.". For the latter, a number of EarthScope-specific features have been added, including locations of proposed USArray (seismic), Plate Boundary Observatory (geodetic), and San Andreas Fault Observatory at Depth sites, plus detailed maps and geographically referenced examples of EarthScope-related scientific investigations. As EarthScope develops, maps will be updated in `real time' so that students of all ages can use the data in formal and informal educational settings.

Geology, Geochronology, and EarthScope: The EarthScope AGeS Program and a new idea for a 4D Earth Initiative

NASA Astrophysics Data System (ADS)

Flowers, R. M.; Arrowsmith, R.; Metcalf, J. R.; Rittenour, T. M.; Schoene, B.; Hole, J. A.; Pavlis, T. L.; Wagner, L. S.; Whitmeyer, S. J.; Williams, M. L.

2015-12-01

The EarthScope AGeS (Awards for Geochronology Student Research) program is a multi-year educational initiative aimed at enhancing interdisciplinary, innovative, and high-impact science by promoting training and new interactions between students, scientists, and geochronology labs at different institutions. The program offers support of up to $10,000 for graduate students to collect and interpret geochronology data that contribute to EarthScope science targets through visits to participating geochronology labs (www.earthscope.org/geochronology). The program was launched by a 2-day short course held before the 2014 National GSA meeting in Vancouver, at which 16 geochronology experts introduced 43 participants to the basic theory and applications of geochronology methods. By the first proposal submission deadline in spring 2015, 33 labs representing a broad range of techniques had joined the program by submitting lab plans that were posted on the EarthScope website. The lab plans provide information about preparation, realistic time frames for visits, and analytical costs. In the first year of the program, students submitted 47 proposals from 32 different institutions. Proposals were ranked by an independent panel, 10 were funded, and research associated with these projects is currently underway. The next proposal deadline will be held in spring 2016. The 4D-Earth initiative is an idea for a natural successor to the EarthScope program aimed at expanding the primarily 3D geophysical focus that captured a snapshot of present day North America into the 4th dimension of time (hence the connection to the prototypical AGeS program), and illuminating the crustal component that was below the resolution of much of the USArray image. Like EarthScope, the notion is that this initiative would integrate new infrastructure and usher in a new way of doing science. The overarching scientific motivation is to develop a Community Geologic Model for the 4-D Evolution of the North American continent to firmly answer long-standing questions of how the time-integrated processes of plate tectonics and surface processes produce the mantle and crustal structures we see today. A breakout session on this topic was held at the 2015 EarthScope National Meeting, and efforts are underway to solicit feedback to shape these ideas.

Integrating EarthScope Data to Constrain the Long-Term Effects of Tectonism on Continental Lithosphere

NASA Astrophysics Data System (ADS)

Porter, R. C.; van der Lee, S.

2017-12-01

One of the most significant products of the EarthScope experiment has been the development of new seismic tomography models that take advantage of the consistent station design, regular 70-km station spacing, and wide aperture of the EarthScope Transportable Array (TA) network. These models have led to the discovery and interpretation of additional compositional, thermal, and density anomalies throughout the continental US, especially within tectonically stable regions. The goal of this work is use data from the EarthScope experiment to better elucidate the temporal relationship between tectonic activity and seismic velocities. To accomplish this, we compile several upper-mantle seismic velocity models from the Incorporated Research Institute for Seismology (IRIS) Earth Model Collaboration (EMC) and compare these to a tectonic age model we compiled using geochemical ages from the Interdisciplinary Earth Data Alliance: EarthChem Database. Results from this work confirms quantitatively that the time elapsed since the most recent tectonic event is a dominant influence on seismic velocities within the upper mantle across North America. To further understand this relationship, we apply mineral-physics models for peridotite to estimate upper-mantle temperatures for the continental US from tomographically imaged shear velocities. This work shows that the relationship between the estimated temperatures and the time elapsed since the most recent tectonic event is broadly consistent with plate cooling models, yet shows intriguing scatter. Ultimately, this work constrains the long-term thermal evolution of continental mantle lithosphere.

Induction Hazard Assessment: The Variability of Geoelectric Responses During Geomagnetic Storms Within Common Hazard Zones

NASA Astrophysics Data System (ADS)

Cuttler, S. W.; Love, J. J.; Swidinsky, A.

2017-12-01

Geomagnetic field data obtained through the INTERMAGNET program are convolved with four validated EarthScope USArray impedances to estimate the geoelectric variations throughout the duration of a geomagnetic storm. A four day long geomagnetic storm began on June 22, 2016, and was recorded at the Brandon (BRD), Manitoba and Fredericksburg (FRD), Virginia magnetic observatories over four days. Two impedance tensors corresponding to each magnetic observatory produce extremely different responses, despite being within close geographical proximity. Estimated time series of the geoelectric field throughout the duration of the geomagnetic storm were calculated, providing an understanding of how the geoelectric field differs across small geographic distances within the same geomagnetic hazard zones derived from prior geomagnetic hazard assessment. We show that the geoelectric response of two sites within 200km of one another can differ by up to two orders of magnitude (4245 mV/km at one location and 38 mV/km at another location 125km away). In addition, we compare these results with estimations of the geoelectric field generated from synthetic 1-dimensional resistivity models commonly used to represent large geographic regions when assessing geomagnetically induced current (GIC) hazards. This comparison shows that estimations of the geomagnetic field from these models differ greatly from estimations produced from Earthscope USArray sites (1205 mV/km in the 1D and 4245 mV/km in the 3D case in one example). This study demonstrates that the application of uniform 1-dimensional resistivity models of the subsurface to wide geographic regions is insufficient to predict the geoelectric hazard at a given location. Furthermore an evaluation of the 3-dimensional resistivity distribution at a given location is necessary to produce a reliable estimation of how the geoelectric field evolves over the course of a geomagnetic storm.

Surprises from the Magnetotelluric Component of the USArray in the Eastern United States: Perplexing Anticorrelations with Seismic Images and Puzzling Insights into Continental Dynamics

NASA Astrophysics Data System (ADS)

Murphy, B. S.; Egbert, G. D.

2017-12-01

In addition to its broadband seismic component, the USArray has also been collecting long-period magnetotelluric (MT) data across the continental United States. These data allow for an unprecedented three-dimensional view of the lithospheric geoelectric structure of the continent. As electrical conductivity and seismic properties provide complementary views of the Earth, synthesizing seismic and MT images can reduce ambiguity inherent in each technique and can thereby allow for tighter constraints on lithospheric properties. In the western US, comparison of MT and seismic results has clarified some issues (e.g., with regard to fluids and volatiles) and has raised some new questions, but for the most part the two techniques provide views that generally mesh well together. In sharp contrast, MT and seismic results in the eastern US lead to seemingly contradictory conclusions about lithosphere properties. The most striking example is the Piedmont region of the southeastern United States; here seismic images suggest a relatively thin, warm Phanerozoic lithosphere, while MT images show a large, deep, highly resistive body that seems to require thick, cold, even cratonic lithosphere. While these MT results shed intriguing new light onto the enigmatic post-Paleozoic history of eastern North America, the strong anticorrelation with seismic images remains a mystery. A similar anticorrelation appears to also exist in the Northern Appalachians, and preliminary views of the geoelectric signature of the well-studied Northern Appalachian Anomaly suggest that synthesizing the seismic and MT images of that region may be nontrivial. Clearly, a major challenge in continued analysis of USArray data is the reconciliation of seemingly contradictory seismic and MT images. The path forward in addressing this problem will require closer collaboration between seismologists and MT scientists and will likely require a careful reconsideration of how each group interprets the physical meaning of their respective anomalies.

Development of a Web Based Simulating System for Earthquake Modeling on the Grid

NASA Astrophysics Data System (ADS)

Seber, D.; Youn, C.; Kaiser, T.

2007-12-01

Existing cyberinfrastructure-based information, data and computational networks now allow development of state- of-the-art, user-friendly simulation environments that democratize access to high-end computational environments and provide new research opportunities for many research and educational communities. Within the Geosciences cyberinfrastructure network, GEON, we have developed the SYNSEIS (SYNthetic SEISmogram) toolkit to enable efficient computations of 2D and 3D seismic waveforms for a variety of research purposes especially for helping to analyze the EarthScope's USArray seismic data in a speedy and efficient environment. The underlying simulation software in SYNSEIS is a finite difference code, E3D, developed by LLNL (S. Larsen). The code is embedded within the SYNSEIS portlet environment and it is used by our toolkit to simulate seismic waveforms of earthquakes at regional distances (<1000km). Architecturally, SYNSEIS uses both Web Service and Grid computing resources in a portal-based work environment and has a built in access mechanism to connect to national supercomputer centers as well as to a dedicated, small-scale compute cluster for its runs. Even though Grid computing is well-established in many computing communities, its use among domain scientists still is not trivial because of multiple levels of complexities encountered. We grid-enabled E3D using our own dialect XML inputs that include geological models that are accessible through standard Web services within the GEON network. The XML inputs for this application contain structural geometries, source parameters, seismic velocity, density, attenuation values, number of time steps to compute, and number of stations. By enabling a portal based access to a such computational environment coupled with its dynamic user interface we enable a large user community to take advantage of such high end calculations in their research and educational activities. Our system can be used to promote an efficient and effective modeling environment to help scientists as well as educators in their daily activities and speed up the scientific discovery process.

Two-year survey comparing earthquake activity and injection-well locations in the Barnett Shale, Texas

PubMed Central

Frohlich, Cliff

2012-01-01

Between November 2009 and September 2011, temporary seismographs deployed under the EarthScope USArray program were situated on a 70-km grid covering the Barnett Shale in Texas, recording data that allowed sensing and locating regional earthquakes with magnitudes 1.5 and larger. I analyzed these data and located 67 earthquakes, more than eight times as many as reported by the National Earthquake Information Center. All 24 of the most reliably located epicenters occurred in eight groups within 3.2 km of one or more injection wells. These included wells near Dallas–Fort Worth and Cleburne, Texas, where earthquakes near injection wells were reported by the media in 2008 and 2009, as well as wells in six other locations, including several where no earthquakes have been reported previously. This suggests injection-triggered earthquakes are more common than is generally recognized. All the wells nearest to the earthquake groups reported maximum monthly injection rates exceeding 150,000 barrels of water per month (24,000 m3/mo) since October 2006. However, while 9 of 27 such wells in Johnson County were near earthquakes, elsewhere no earthquakes occurred near wells with similar injection rates. A plausible hypothesis to explain these observations is that injection only triggers earthquakes if injected fluids reach and relieve friction on a suitably oriented, nearby fault that is experiencing regional tectonic stress. Testing this hypothesis would require identifying geographic regions where there is interpreted subsurface structure information available to determine whether there are faults near seismically active and seismically quiescent injection wells. PMID:22869701

Earthquake Source Parameter Estimates for the Charlevoix and Western Quebec Seismic Zones in Eastern Canada

NASA Astrophysics Data System (ADS)

Onwuemeka, J.; Liu, Y.; Harrington, R. M.; Peña-Castro, A. F.; Rodriguez Padilla, A. M.; Darbyshire, F. A.

2017-12-01

The Charlevoix Seismic Zone (CSZ), located in eastern Canada, experiences a high rate of intraplate earthquakes, hosting more than six M >6 events since the 17th century. The seismicity rate is similarly high in the Western Quebec seismic zone (WQSZ) where an MN 5.2 event was reported on May 17, 2013. A good understanding of seismicity and its relation to the St-Lawrence paleorift system requires information about event source properties, such as static stress drop and fault orientation (via focal mechanism solutions). In this study, we conduct a systematic estimate of event source parameters using 1) hypoDD to relocate event hypocenters, 2) spectral analysis to derive corner frequency, magnitude, and hence static stress drops, and 3) first arrival polarities to derive focal mechanism solutions of selected events. We use a combined dataset for 817 earthquakes cataloged between June 2012 and May 2017 from the Canadian National Seismograph Network (CNSN), and temporary deployments from the QM-III Earthscope FlexArray and McGill seismic networks. We first relocate 450 events using P and S-wave differential travel-times refined with waveform cross-correlation, and compute focal mechanism solutions for all events with impulsive P-wave arrivals at a minimum of 8 stations using the hybridMT moment tensor inversion algorithm. We then determine corner frequency and seismic moment values by fitting S-wave spectra on transverse components at all stations for all events. We choose the final corner frequency and moment values for each event using the median estimate at all stations. We use the corner frequency and moment estimates to calculate moment magnitudes, static stress-drop values and rupture radii, assuming a circular rupture model. We also investigate scaling relationships between parameters, directivity, and compute apparent source dimensions and source time functions of 15 M 2.4+ events from second-degree moment estimates. To the first-order, source dimension estimates from both methods generally agree. We observe higher corner frequencies and higher stress drops (ranging from 20 to 70 MPa) typical of intraplate seismicity in comparison with interplate seismicity. We follow similar approaches to studying 25 MN 3+ events reported in the WQSZ using data recorded by the CNSN and USArray Transportable Array.

Seismically imaging the structural legacy of rifting and collision events in the central and eastern U.S. crust

NASA Astrophysics Data System (ADS)

Schmandt, B.; Lin, F. C.; Karlstrom, K. E.

2015-12-01

EarthScope's USArray now provides broadband seismic data across the contiguous U.S. and southeastern Canada. We used teleseismic receiver functions and surface wave tomography to map crustal structure beneath the entire array. Crust thickness was estimated with multi-mode Ps receiver function images using <0.5 Hz Ps and <0.25 Hz 2p1s and 2s1p reverberations between the free-surface and Moho. In areas of sedimentary basins or large impedance contrasts in the middle crust the reverberations alone often provide clearer images of the Moho than the Ps mode, because of interference from conversions at shallow interfaces is reduced at greater lag times. The new results enable large-scale comparison of the structural legacy of multiple rifting and collision events in eastern North America. Some Proterozoic rift segments defined by Bouguer gravity and surface geology maintain locally thin crust while others lack correlated Moho topography or are areas of locally thicker crust. Locally thin crust is found at southern end of the mid-continent rift (MCR) in northern Kansas and southern Nebraska, along the Reelfoot rift, and beneath inferred rifts in Michigan, Indiana, and Ohio. The Oklahoma aulacogen is not associated with a coherent change in crust thickness along its length, at least at a scale resolvable by USArray data and our imaging approach. The MCR extending northeast from Nebraska to Lake Superior has locally thicker crust, consistent with other recent results. We suggest that magmatic additions to the lower crust overwhelmed extension in the northern mid-continent rift, but not the rift segments further south and east. Collision events of the Grenville orogeny and Paleozoic orogens that created the Appalachian Mountains are still associated with ~45-55 km thick crust extending from the Grenville front eastward across the Appalachian Mountains to the fall line that marks the abrupt geomorphic transition to the coastal plains. Despite the ~45-55 km crust thickness long-wavelength elevations (>50 km) across this area rarely exceed 1 km. Along the fall line we find ~15-20 km of seaward thinning that is coherent from Alabama to Pennsylvania, with a transition width similar to or less than the ~70 km.

Possible origin of the Bighorn uplift, WY, by lithospheric buckling during the Laramide orogeny

NASA Astrophysics Data System (ADS)

Tikoff, B.; Siddoway, C. S.; Worthington, L. L.; Anderson, M. L.

2017-12-01

The EarthScope Bighorn Project investigated the Bighorn uplift, Wyoming, a foreland structure developed during the 75-55 Ma Laramide orogeny. Any model for the Bighorn uplift must account for several geological and geophysical results from the EarthScope broadband and passive-active seismic study, the broader context provided by USArray, and legacy datasets: 1) The Moho is bulged up below portions of the surface exposure of the basement arch; 2) a high-velocity, high-density material (the "7.x layer") is absent in the lower crust beneath the arch culmination; 3) Shear wave splitting analysis shows distinct mantle fabrics on either side of the uplift; 4) Crustal thicknesses varied widely prior to the Laramide-age deformation; 5) A lack of reflectors associated with a regional decollement; 6) The Bighorn arch forms one in an array of low-amplitude, large-wavelength folds throughout the High Plains region. The uplift borders a NNW-trending (E-dipping?) geophysical anomaly inferred to be Proterozoic suture. A lithospheric buckling model offers a framework that accommodates most of the geological and geophysical data. Lithospheric buckling is the concept of low-amplitude, large-wavelength (150-350 km) lithospheric folding developed in response to an end-load, replicated in scaled physical models. A buckling instability focuses initial deformation, with faults developed in layered media/crustal section as shortening progresses. The strength/age of the mantle controls the fold wavelength, based on examples from multiple orogens (e.g. Urals, central Asia). Rarely does the geometry of the upward Moho deflection identically mirror the surface uplift in scaled models, nor does it in the Bighorn uplift, where fold localization is likely controlled by a pre-existing Proterozoic suture and/or mantle asperity. Indicated by shear wave SKS splitting data, distinct mantle fabrics on either side of the uplift extend into the lithospheric mantle, indicated the presence of a deep-rooted structure of a type that has not been incorporated in physical models.

Linking ShakeMap and Emergency Managers in the Utah Region

NASA Astrophysics Data System (ADS)

Pankow, K.; Bausch, D.; Carey, B.

2007-12-01

In 2001, the University of Utah Seismograph Stations (UUSS) locally customized and began producing automatic ShakeMaps in Utah's Wasatch Front urban corridor as part of a new real-time earthquake information system developed under the Advanced National Seismic System. In 2005, motivated by requests from Utah's Division of Homeland Security and FEMA, ShakeMap capabilities were expanded to cover the entire Utah region. Now in 2007, ShakeMap capabilities throughout the region will again be enhanced by increased station coverage. The increased station coverage comes both from permanent stations funded by a state initiative and from the temporary deployment of EarthScope USArray stations. The state initiative will add ~22 strong-motion instruments and ~10 broadband instruments to the UUSS network. The majority of these stations will be located in southwestern Utah--one of the fastest growing regions in the U.S. EarthScope will evenly distribute 70 broadband stations in the region during 2007 that will be removed after 18 to 24 months. In addition to the enhanced station coverage for producing ShakeMaps in the Utah region, the transfer of information to the emergency response community is also being enhanced. First, tools are being developed that will link ShakeMap data with HAZUS loss-estimation software in near-real-time for rapid impact assessment. Second, ShakeMap scenarios are being used in conjunction with HAZUS loss-estimation software to produce customized maps for planning and preparedness exercises and also for developing templates that can be used following a significant regional earthquake. With the improvements to ShakeMap and the improved dialogue with the emergency managers, a suite of maps and information products were developed based on scenario earthquakes for training and exercise purposes. These products will be available in a timely fashion following a significant earthquake in the Utah region.

Mapping the Influence of Prior Tectonism on Seismicity in the Central and Eastern US

NASA Astrophysics Data System (ADS)

Boyd, O. S.; Levandowski, W.; Ramirez-Guzman, L.; Zellman, M.; Briggs, R.

2015-12-01

From the Atlantic margin to the Rockies, most earthquakes in the central and eastern U.S. occur in ancient tectonic zones, yet many such features have been historically quiescent. If all intraplate stress were transferred from plate boundaries or bases, the stress field would be broadly uniform, with all well-oriented faults equally likely to slip. But faults are not the only product of tectonism; intrusions, metamorphism, or any number of other alterations may modify crustal and/or upper mantle density, leaving behind lithostatic pressure gradients that can locally elevate or reduce stress on faults. With data provided by Earthscope, we are working to map lithospheric density across the U.S. and to quantify gravitational body-forces using analytical and finite-element methods. Regional-scale 3D models show that gravitational forces focus seismicity and reorient principal stress both in the New Madrid seismic zone and the western Great Plains. Sedimentary fill and low elevation encourage Reelfoot Rift-normal contraction, yet along-strike variations in lower crustal density rotate body-forces beneath New Madrid to interfere constructively with far-field compression, augmenting differential stress by 5-10 MPa. On the plains of SE Colorado and SE Wyoming, the Cheraw and Wheatland/Whalen faults collocate with multiply reactivated Proterozoic sutures, enigmatic Quaternary extension, and focused seismicity with regionally anomalous NW-SE moment tensor T-axes. Earthscope data help reveal anomalously buoyant lower crust beneath each suture -­- which we hypothesize reflects hydration by Farallon slab-derived fluids that have preferentially migrated along ancient fracture networks -- that generates 10 MPa of localized suture-normal tension, consistent with geomorphic strain- and seismic stress-indicators. As continent-wide seismic models emerge from Earthscope data, we will continue to map regions where inherited structures encourage intraplate seismicity.

Real-time operation of the NSF EarthScope USArray Transportable Array

NASA Astrophysics Data System (ADS)

Astiz, L.; Eakins, J. A.; Vernon, F. L.; Martynov, V.; Newman, R. L.; Cox, T. A.; Mulder, T. L.; Busby, R. W.

2007-05-01

The Transportable Array (TA) component of USArray uses real-time telemetry to send data to the Array Network Facility (ANF) through a variety of satellite, mobile phone, wireless and wired communication links. The ANF is responsible for the timely delivery of metadata and waveform data to the IRIS DMC from the growing number of Transportable Array stations. The IRIS DMC makes these data available to the research community. The network has increased in size to 327 stations with 259 out of the 400 new TA sites installed (as of 28 February 2007). Starting in Fall 2007, equipment will start to roll from current stations to new locations to the east of the current footprint. Use of the Antelope software package has allowed the ANF to maintain and operate this extremely dynamic network configuration, facilitating the collection and transfer of data, the generation and merging of the metadata as well as the real-time monitoring of state of health of TA station data-loggers and their command and control. Four regional networks (ANZA, BDSN, SCSN, and UNR) as well as the USNSN contribute data to the Transportable Array in real-time. Although the real-time data flow to the IRIS DMC has been 93.4% over the last year, the ANF and the TA field teams have extended every effort and have managed to recover an additional 4.8% by recovering data from the local data storage device (Baler 14) at each station. Once the missing data is recovered, we then generate station-channel-day volume seed files, which are resent to the DMC to bring the total data recovery rate to 98.4%. The total network uptime is above 99%. Analyst review of automatic locations for the USArray network is being done at the ANF as part of the data quality monitoring strategy. All events are associated with the USGS and regional network bulletins. As of February 2007, around 13,000 weekly picks are being fully reviewed by analysts at the ANF and over 19,000 events have been recorded. We find a small percentage (about 10 %) of events that cannot be associated with existing bulletins. This information is used by the regional network operators to help them determine which TA stations may be beneficial to permanently add to their seismic networks. Operation of the USArray at the ANF has benefited by the real-time interface with the ORB and the Datascope database using PHP for display on the ANF website (http:anf.ucsd.edu) to provide station and system state-of- health information to field teams. Information available for all stations includes: location, maps, photographs, equipment deployed, communications, distribution of events recorded by each station, and displays of daily, weekly, and yearly state of health parameters as well as station noise spectra generated by the DMC.

Detection and analysis of a transient energy burst with beamforming of multiple teleseismic phases

NASA Astrophysics Data System (ADS)

Retailleau, Lise; Landès, Matthieu; Gualtieri, Lucia; Shapiro, Nikolai M.; Campillo, Michel; Roux, Philippe; Guilbert, Jocelyn

2018-01-01

Seismological detection methods are traditionally based on picking techniques. These methods cannot be used to analyse emergent signals where the arrivals cannot be picked. Here, we detect and locate seismic events by applying a beamforming method that combines multiple body-wave phases to USArray data. This method explores the consistency and characteristic behaviour of teleseismic body waves that are recorded by a large-scale, still dense, seismic network. We perform time-slowness analysis of the signals and correlate this with the time-slowness equivalent of the different body-wave phases predicted by a global traveltime calculator, to determine the occurrence of an event with no a priori information about it. We apply this method continuously to one year of data to analyse the different events that generate signals reaching the USArray network. In particular, we analyse in detail a low-frequency secondary microseismic event that occurred on 2010 February 1. This event, that lasted 1 d, has a narrow frequency band around 0.1 Hz, and it occurred at a distance of 150° to the USArray network, South of Australia. We show that the most energetic phase observed is the PKPab phase. Direct amplitude analysis of regional seismograms confirms the occurrence of this event. We compare the seismic observations with models of the spectral density of the pressure field generated by the interferences between oceanic waves. We attribute the observed signals to a storm-generated microseismic event that occurred along the South East Indian Ridge.

Informal Geoscience Education partnerships via the EarthScope Program

NASA Astrophysics Data System (ADS)

Lillie, R. J.; Trehu, A. M.; Goddard, C.; Braunmiller, J.

2008-05-01

EarthScope is a National Science Foundation (NSF)-supported program to explore the structure and evolution of the North American continent and understand the processes controlling earthquakes and volcanic eruptions. It consists of three observatories, funded through NSF's Major Research Equipment and Facilities Construction program. 1) The Plate Boundary Observatory (PBO) consists of GPS and other geodetic instruments to measure deformation of the active plate boundary that characterizes the western United States. 2) The San Andreas Fault Observatory at Depth (SAFOD) is a hole drilled to sample and instrument an active strand of an earthquake fault. 3) USArray is a network of seismometers and other geophysical instruments to record earthquakes and image the velocity and electrical conductivity structure from the Pacific to the Atlantic oceans. This nationwide recording effort and large-scale scientific objective provides a unique opportunity to partner with the U. S. National Park Service and other state, federal and private organizations that inform the public about the natural world. In particular, the EarthScope National Office (ESNO) is developing thematic displays to link multiple parks through their common geodynamic origin. These displays are being tested and refined through a series of workshops during which park and museum personnel, K-12 teachers, and active research scientists work together to develop programs to introduce the public to the forces that shape our continent. The first of these workshops, held in April, 2008, at the Mount Rainier National Park Education Center in Washington State, focused on earthquake, volcanic, and other tectonic processes that form the dynamic landscape of the Pacific Northwest.

EarthScope's Transportable Array in Alaska and Western Canada

NASA Astrophysics Data System (ADS)

Enders, M.; Miner, J.; Bierma, R. M.; Busby, R.

2015-12-01

EarthScope's Transportable Array (TA) in Alaska and Canada is an ongoing deployment of 261 high quality broadband seismographs. The Alaska TA is the continuation of the rolling TA/USArray deployment of 400 broadband seismographs in the lower 48 contiguous states and builds on the success of the TA project there. The TA in Alaska and Canada is operated by the IRIS Consortium on behalf of the National Science Foundation as part of the EarthScope program. By Sept 2015, it is anticipated that the TA network in Alaska and Canada will be operating 105 stations. During the summer 2015, TA field crews comprised of IRIS and HTSI station specialists, as well as representatives from our partner agencies the Alaska Earthquake Center and the Alaska Volcano Observatory and engineers from the UNAVCO Plate Boundary Observatory will have completed a total of 36 new station installations. Additionally, we will have completed upgrades at 9 existing Alaska Earthquake Center stations with borehole seismometers and the adoption of an additional 35 existing stations. As the array doubles in Alaska, IRIS continues to collaborate closely with other network operators, universities and research consortia in Alaska and Canada including the Alaska Earthquake Center (AEC), the Alaska Volcano Observatory (AVO), the UNAVCO Plate Boundary Observatory (PBO), the National Tsunami Warning Center (NTWC), Natural Resources Canada (NRCAN), Canadian Hazard Information Service (CHIS), the Yukon Geologic Survey (YGS), the Pacific Geoscience Center of the Geologic Survey, Yukon College and others. During FY14 and FY15 the TA has completed upgrade work at 20 Alaska Earthquake Center stations and 2 AVO stations, TA has co-located borehole seismometers at 5 existing PBO GPS stations to augment the EarthScope observatory. We present an overview of deployment plan and the status through 2015. The performance of new Alaska TA stations including improvements to existing stations is described.

Expedition Earthscope: A Television Film and DVD

NASA Astrophysics Data System (ADS)

Prose, D.; Lamacchia, D.

2005-12-01

Independent filmmakers are producing a public television documentary that explores the goals and aspirations of the Earthscope project in the context of what is known and not known about the geology of North America. The unfolding story captures the excitement of the early stages of an historic expedition undertaken by a diverse group of scientists, students, and volunteers, employing the most advanced earth exploration techniques to answer persistent geologic questions about the North American continent. The film documents the efforts of Earthscope scientists as participants in one of the largest coordinated geologic experiments ever, one that promises to deepen our knowledge of the processes, including seismic and volcanic, that have formed the continent and its spectacular landforms. Interspersed with scenes of scientists beginning new Earthscope experiments is archival footage of past experiments, as well as dramatic scenes of earthquakes, volcanic eruptions, landscapes, and cultural activities filmed throughout the US. The film's liberal use of 3D animations helps explain the geologic story and the techniques employed by Earthscope scientists. The purpose of the documentary is to introduce Earthscope and basic earth science concepts to a nationwide audience via PBS broadcasts and distribution to schools, libraries, science centers, and museums. For Earthscope staff, scientists, and educators, the film will be a tool to help educate the public about Earthscope and recruit a diverse mix of young people to take part in the effort. To enhance the usefulness of the film, a companion DVD is also being produced that will include printable ancillary educational resources for use in classrooms and materials that explain the Earthscope project in detail. Pre-release clips from the film will be shown and distribution plans discussed.

Great Earthquakes and Tsunami Day for Teachers on the Leading Edge: Geologic Hazards and Links to EarthScope in a Field-Based Program

NASA Astrophysics Data System (ADS)

Butler, R.; Bishop, E. M.; Ault, C.; Magura, B.; Hedeen, C.; Connor, D.; Southworth-Neumeyer, T.; Conrey, R.

2005-12-01

Inviting K-12 science teachers into the field to observe the work of professional geologists and engage in learning that is scientifically important and socially relevant deepens their geologic understanding while instilling enthusiasm for inquiry-based instruction. "Teachers on the Leading Edge" (TOTLE) is a field-based and place-based teacher development program that features active continental margin geology of the Pacific Northwest. Program themes include: (1) Geophysics as fundamental to understanding plate tectonics and essential to deciphering Pacific Northwest geology that underlies a tree-covered landscape; and (2) Geologic Hazards as understandable and inevitable consequences of living on the leading edge of our continent. The two-week TOTLE 2005 field workshop traversed the active continental margin of Oregon from the Pacific Coast through the Cascade Range to accreted terranes along the Snake River. "Great Earthquakes and Tsunami Day" featured introductions to earthquake seismology and paleoseismology. Presentations on earthquake seismology with examples from the December 2004 Sumatra - Andaman earthquake and Indian Ocean tsunami provided context and background. During a morning low tide near Fort Clatsop south of Astoria, paleoseismologist Brian Atwater (USGS, Seattle) helped teachers observe and interpret drowned forests and tsunami deposits that mark four great Cascadia earthquakes of the past 2000 years. That afternoon, Darci Connor, former Tsunami Outreach Coordinator for the City of Seaside, helped teachers understand their critical role in educating K-12 students about natural hazard preparedness. In the evening, TOTLE teachers crafted their new understanding of great earthquakes and tsunami into interactive learning activities for Science Campers at Camp Kiwanilong operated by the Oregon Museum of Science and Industry. These experiences make frontier geophysical research, like GPS observations of slow earthquakes and seismic tomography of the subducting Juan de Fuca Plate, accessible to K-12 teachers and useful in their teaching of plate tectonics and earthquake seismology. Teachers on the Leading Edge is preparing K-12 teachers to convey the importance and discoveries of EarthScope's USArray and Plate Boundary Observatory experiments to their students.

Insights on Lithospheric Foundering from the Sierra Nevada Earthscope Project (SNEP)

NASA Astrophysics Data System (ADS)

Zandt, G.; Gilbert, H.; Frassetto, A.; Owens, T.; Jones, C.

2004-12-01

Interdisciplinary studies in the southern Sierra Nevada have documented an ongoing removal of the dense residual root from beneath the southern Sierra Nevada batholith. However, many questions remain concerning the timing, spatial extent, mechanism, and consequences of this lithospheric foundering event. The Sierra Nevada Earthscope Project (SNEP) is a scientific experiment designed to investigate these questions with a 2- phase (2 year) seismic deployment of 46 broadband Flex-Array stations embedded in the existing stations of the USArray Transportable Array (TA) in the region. In the 2 phases, approximately 80 sites have been occupied from the northern edge of Kings Canyon north to Honey Lake and from the Central Valley into the Great Basin. In this presentation, we will focus on the most recent common-conversion-point (CCP) stacks of the receiver functions that provide a 3D image of lithospheric layering beneath the central and northern Sierra Nevada. Examining sequential cross-sections reveals distinctive lithospheric "reflectivity" patterns that characterize different tectonic imprints. From phase 1 data, we observed that the westernmost Basin and Range exhibits strong layering with multiple low-velocity zones in the crust and uppermost mantle and a relatively flat and strong Moho varying slowly in depth between 30 and 35 km. In the south this Basin and Range character terminates on the eastern edge of the Sierra Nevada; however, north of Big Pine the Basin and Range character intrudes progressively farther into the range and ends up more than 50 km west of the eastern edge of the range. The lithosphere beneath the southern high Sierra Nevada is characterized by a relatively transparent (homogeneous) crust and sharp Moho that disappears westward beneath the adjacent foothills. The crustal thickness in this area is mostly between 30-35 km with localized welts of thicker crust. The phase 1 observations imply that the removal process appears to be actively affecting the crust northward through at least the central Sierra Nevada. The phase 2 deployment provides coverage to the northern limit of the Sierra Nevada to determine the extent of the affected region and the character of the batholith where root removal may or may not have occurred.

Insights on Lithospheric Foundering from the Sierra Nevada Earthscope Project (SNEP)

NASA Astrophysics Data System (ADS)

Zandt, G.; Gilbert, H.; Frassetto, A.; Owens, T.; Jones, C.

2007-12-01

Interdisciplinary studies in the southern Sierra Nevada have documented an ongoing removal of the dense residual root from beneath the southern Sierra Nevada batholith. However, many questions remain concerning the timing, spatial extent, mechanism, and consequences of this lithospheric foundering event. The Sierra Nevada Earthscope Project (SNEP) is a scientific experiment designed to investigate these questions with a 2- phase (2 year) seismic deployment of 46 broadband Flex-Array stations embedded in the existing stations of the USArray Transportable Array (TA) in the region. In the 2 phases, approximately 80 sites have been occupied from the northern edge of Kings Canyon north to Honey Lake and from the Central Valley into the Great Basin. In this presentation, we will focus on the most recent common-conversion-point (CCP) stacks of the receiver functions that provide a 3D image of lithospheric layering beneath the central and northern Sierra Nevada. Examining sequential cross-sections reveals distinctive lithospheric "reflectivity" patterns that characterize different tectonic imprints. From phase 1 data, we observed that the westernmost Basin and Range exhibits strong layering with multiple low-velocity zones in the crust and uppermost mantle and a relatively flat and strong Moho varying slowly in depth between 30 and 35 km. In the south this Basin and Range character terminates on the eastern edge of the Sierra Nevada; however, north of Big Pine the Basin and Range character intrudes progressively farther into the range and ends up more than 50 km west of the eastern edge of the range. The lithosphere beneath the southern high Sierra Nevada is characterized by a relatively transparent (homogeneous) crust and sharp Moho that disappears westward beneath the adjacent foothills. The crustal thickness in this area is mostly between 30-35 km with localized welts of thicker crust. The phase 1 observations imply that the removal process appears to be actively affecting the crust northward through at least the central Sierra Nevada. The phase 2 deployment provides coverage to the northern limit of the Sierra Nevada to determine the extent of the affected region and the character of the batholith where root removal may or may not have occurred.

New Data Products Available at the IRIS Data Management Center

NASA Astrophysics Data System (ADS)

Ahern, T.; Casey, R.; Kamb, L.; Zeleznik, M.; Ammon, C. J.

2007-12-01

With USArray data processing and services in full production, the IRIS Data Management Center (DMC) has developed an online tool to function as a library for products derived from raw USArray observations as well as other catalogs with broad interest produced and supplied by the geoscience community. The service, called SPADE, is a flexible, annotated cataloging system for storing heterogeneous data products supplied by registered providers. SPADE includes a web interface that allows users to search across the spectrum of varied data products using geographic, temporal, and/or keyword parameters to locate products of specific interest. In addition to cooperative product submissions from outside institutions, the IRIS DMC is collaborating and developing frameworks to produce and to provide interesting products that take advantage of data from USArray sensors. These products are automatically produced in near- real time following interesting seismic events, and broaden the range of information that IRIS delivers to the geoscience community. In this presentation we will demonstrate the SPADE query interface and present examples of the available data products such as Global Centroid Moment Tensor solutions from Harvard and Columbia Universities, historic earthquake data scanned from select WWSSN film chips, as well as IRIS-produced seismic record sections, and ground-motion animations derived from Transportable Array observations.

Crustal and Uppermost Mantle Structure beneath the Western United States from USArray Regional Phase Analysis

NASA Astrophysics Data System (ADS)

Buehler, Janine Sylvia

The aim of this dissertation is to improve our understanding of the crust and uppermost mantle structure in the western United States, profiting from the wealth of regional phase data recorded at USArray stations. USArray, a transportable seismic array of ˜400 seismometers, has greatly increased seismic data coverage across the United States in the past few years, and allows imaging of the lithosphere of the North American continent with better resolution and new methods. The regional phases are often challenging to analyze, especially in a tectonically-active region like the western United States, because of their sensitivities to the heterogeneities of the crust and uppermost mantle. However, knowledge of the seismic structure of the lithosphere is not only essential in order to accurately image the velocity structure at greater depths, but also for constraining geodynamic models that reconstruct the tectonic evolution of the continent, and hence the information that is carried by the regional phases is very valuable. The data set used in this study consists mostly of the regional seismic phases Pn and Sn, which propagate horizontally along the Moho in the mantle lid and constrain the seismic velocity structure at a confined depth. We applied traditional tomographic methods that profit from the improved ray coverage through USArray, but also employed array-based techniques that take advantage of the regular station spacing of the transportable array and don't depend on regularization. In addition, we used stacking methods to image the propagation efficiency of the Sn phase, which is often highly attenuated in tectonically active regions, on a regional scale. The results complement other seismic studies that average over greater depth intervals, such as surface- and body-wave tomographies and anisotropy analysis from shear-wave splitting, to provide information on temperature, composition, and tectonic processes at depth. Comparisons between Pn azimuthal anisotropy and fast polarization direction from shear wave splitting suggest significant vertical changes in anisotropy in several regions of the upper mantle beneath the western United States. Sn can in theory further constrain the nature of anisotropy in the mantle lid. However, we have so far been unable to resolve shear-wave splitting directly in the Sn waveforms as the phase is often attenuated and difficult to detect. Still, we obtained evidence for Sn propagation in several regions of the western United States such as the central Great Basin and the northeastern part of the Colorado Plateau. We found that there are enough quality Sn picks for joint Pn-Sn tomography and identified prominent Vp/Vs anomalies, such as large high Vp/Vs regions --- typically associated with partial melt --- below the Snake River Plain and the Colorado Plateau.

Technology and Engineering Advances Supporting EarthScope's Alaska Transportable Array

NASA Astrophysics Data System (ADS)

Miner, J.; Enders, M.; Busby, R.

2015-12-01

EarthScope's Transportable Array (TA) in Alaska and Canada is an ongoing deployment of 261 high quality broadband seismographs. The Alaska TA is the continuation of the rolling TA/USArray deployment of 400 broadband seismographs in the lower 48 contiguous states and builds on the success of the TA project there. The TA in Alaska and Canada is operated by the IRIS Consortium on behalf of the National Science Foundation as part of the EarthScope program. By Sept 2015, it is anticipated that the TA network in Alaska and Canada will be operating 105 stations. During the summer of 2015, TA field crews comprised of IRIS and HTSI station specialists, as well as representatives from our partner agencies the Alaska Earthquake Center and the Alaska Volcano Observatory and engineers from the UNAVCO Plate Boundary Observatory will have completed a total of 36 new station installations. Additionally, we will have completed upgrades at 9 existing Alaska Earthquake Center stations with borehole seismometers and the adoption of an additional 35 existing stations. Continued development of battery systems using LiFePO4 chemistries, integration of BGAN, Iridium, Cellular and VSAT technologies for real time data transfer, and modifications to electronic systems are a driving force for year two of the Alaska Transportable Array. Station deployment utilizes custom heliportable drills for sensor emplacement in remote regions. The autonomous station design evolution include hardening the sites for Arctic, sub-Arctic and Alpine conditions as well as the integration of rechargeable Lithium Iron Phosphate batteries with traditional AGM batteries We will present new design aspects, outcomes, and lessons learned from past and ongoing deployments, as well as efforts to integrate TA stations with other existing networks in Alaska including the Plate Boundary Observatory and the Alaska Volcano Observatory.

The Influence of Geography and Geology on Seismic Background Noise Levels Across the United States as Revealed by the Transportable Array

NASA Astrophysics Data System (ADS)

Anthony, R. E.; Ringler, A. T.; Holland, A. A.; Wilson, D. C.

2017-12-01

The EarthScope USArray Transportable Array (TA) has now covered the US with 3-component broadband seismometers at approximately 70 km station spacing and deployment durations of approximately 2 years. This unprecedented coverage, combined with high-quality and near homogenous installation techniques, offers a novel dataset in which to characterize spatially varying levels of background seismic noise across the United States. We present background noise maps in period bands of interest to earthquake and imaging seismology across the US (lower 48 states and Alaska). Early results from the contiguous 48 states demonstrate that ambient noise levels within the body wave period band (1-5 s) vary by > 20 dB (rel. 1 (m/s2)2/Hz) with the highest noise levels occurring at stations located within sedimentary basins and lowest within the mountain ranges of the Western US. Additionally, stations around the Great Lakes observe heightened noise levels in this band beyond the aforementioned basin amplification. We attribute this observation to local swell activity in the Great Lakes generating short-period microseism signals. This suggests that lake-generated microseisms may be a significant source of noise for Alaskan deployments situated in close proximity to lakes to facilitate float plane access. We further investigate how basin amplification and short-period lake microseism signals may noticeably impact detection and signal-to-noise of teleseismic body wave signals during certain time periods. At longer-periods (> 20 s), we generally observe larger noise levels on the horizontal components of stations situated in basins or on soft sediment, likely caused by locally induced tilt of the sensor. We will present similar analysis from the initial Alaska TA dataset to quantitatively assess how utilization of posthole sensors affects signal-to-noise for the long-period horizontal wavefield.

EMERALD: Coping with the Explosion of Seismic Data

NASA Astrophysics Data System (ADS)

West, J. D.; Fouch, M. J.; Arrowsmith, R.

2009-12-01

The geosciences are currently generating an unparalleled quantity of new public broadband seismic data with the establishment of large-scale seismic arrays such as the EarthScope USArray, which are enabling new and transformative scientific discoveries of the structure and dynamics of the Earth’s interior. Much of this explosion of data is a direct result of the formation of the IRIS consortium, which has enabled an unparalleled level of open exchange of seismic instrumentation, data, and methods. The production of these massive volumes of data has generated new and serious data management challenges for the seismological community. A significant challenge is the maintenance and updating of seismic metadata, which includes information such as station location, sensor orientation, instrument response, and clock timing data. This key information changes at unknown intervals, and the changes are not generally communicated to data users who have already downloaded and processed data. Another basic challenge is the ability to handle massive seismic datasets when waveform file volumes exceed the fundamental limitations of a computer’s operating system. A third, long-standing challenge is the difficulty of exchanging seismic processing codes between researchers; each scientist typically develops his or her own unique directory structure and file naming convention, requiring that codes developed by another researcher be rewritten before they can be used. To address these challenges, we are developing EMERALD (Explore, Manage, Edit, Reduce, & Analyze Large Datasets). The overarching goal of the EMERALD project is to enable more efficient and effective use of seismic datasets ranging from just a few hundred to millions of waveforms with a complete database-driven system, leading to higher quality seismic datasets for scientific analysis and enabling faster, more efficient scientific research. We will present a preliminary (beta) version of EMERALD, an integrated, extensible, standalone database server system based on the open-source PostgreSQL database engine. The system is designed for fast and easy processing of seismic datasets, and provides the necessary tools to manage very large datasets and all associated metadata. EMERALD provides methods for efficient preprocessing of seismic records; large record sets can be easily and quickly searched, reviewed, revised, reprocessed, and exported. EMERALD can retrieve and store station metadata and alert the user to metadata changes. The system provides many methods for visualizing data, analyzing dataset statistics, and tracking the processing history of individual datasets. EMERALD allows development and sharing of visualization and processing methods using any of 12 programming languages. EMERALD is designed to integrate existing software tools; the system provides wrapper functionality for existing widely-used programs such as GMT, SOD, and TauP. Users can interact with EMERALD via a web browser interface, or they can directly access their data from a variety of database-enabled external tools. Data can be imported and exported from the system in a variety of file formats, or can be directly requested and downloaded from the IRIS DMC from within EMERALD.

A Dramatic Increase in Seismic Observations in the Central and Eastern US

NASA Astrophysics Data System (ADS)

Woodward, R.; Busby, R.; Simpson, D.; Alvarez, M.; Vernon, F.

2009-05-01

The USArray Transportable Array (TA) is a network of 400 seismograph stations that is systematically moving west-to-east across the contiguous United States. The TA is part of the National Science Foundation's multi- disciplinary EarthScope program. The TA has already occupied over 700 stations in the western US, and is continuing its multi-year migration towards the Atlantic coast before heading for Alaska. The stations use a grid-like deployment with 70 km separation between stations. At any given time there are approximately 400 stations operational, occupying a nominal 800 km by 2000 km "footprint." Each station is operated for two years. TA stations consist of three component broadband seismometers, with a few sites in the westernmost United States also including three component strong motion instruments. The instruments are installed about two meters below the surface, in thermally stable vaults. All stations transmit continuous data in near-real-time, and the data are freely distributed through the IRIS Data Management Center. TA stations can be upgraded to incorporate high frequency or strong motion instrument. Organizations can also "adopt" stations after installation by reimbursing the cost of the hardware, so that the stations become permanent. The TA is presently operating in the swath of the country extending from Texas to Montana. From 2010 to 2013 the TA will occupy ~800 sites in the central and eastern US. The array will be centered on the New Madrid, MO region during the bicentennial of the 1811-1812 earthquakes. During the TA deployment every existing or planned nuclear plant in the eastern US will be within 70 km of at least four new seismic stations. Thus, this station deployment in the eastern half of the US presents an unprecedented opportunity for improving source characterization, modeling the regional velocity and attenuation structure, and mapping seismic zones down to low magnitude thresholds. We will provide an overview of TA installation plans, instrumentation, and data so that scientists and decision makers are better prepared to capitalize on the unique opportunity presented by the TA moving through the central and eastern US. We will provide examples of TA station performance, as well as examples of data quality and seismic detection thresholds observed in the western US.

Broadening the Quality and Capabilities of the EarthScope Alaska Transportable Array

NASA Astrophysics Data System (ADS)

Busby, R. W.

2016-12-01

In 2016, the EarthScope Transportable Array (TA) program will have 195 broadband seismic stations operating in Alaska and western Canada. This ambitious project will culminate in a network of 268 new or upgraded real-time seismic stations operating through 2019. The challenging environmental conditions and the remoteness of Alaska have motivated a new method for constructing a high-quality, temporary seismic network. The Alaska TA station design builds on experience of the Lower 48 TA deployment and adds design requirements because most stations are accessible only by helicopter. The stations utilize new high-performance posthole sensors, a specially built hammer/auger drill, and lightweight lithium ion batteries to minimize sling loads. A uniform station design enables a modest crew to build the network on a short timeline and operate them through the difficult conditions of rural Alaska. The Alaska TA deployment has increased the quality of seismic data, with some well-sited 2-3 m posthole stations approaching the performance of permanent Global Seismic Network stations emplaced in 100 m boreholes. The real-time data access, power budget, protective enclosure and remote logistics of these TA stations has attracted collaborations with NASA, NOAA, USGS, AVO and other organizations to add auxiliary sensors to the suite of instruments at many TA stations. Strong motion sensors have been added to (18) stations near the subduction trench to complement SM stations operated by AEC, ANSS and GSN. All TA and most upgraded stations have pressure and infrasound sensors, and 150 TA stations are receiving a Vaisala weather sensor, supplied by the National Weather Service Alaska Region and NASA, capable of measuring temperature, pressure, relative humidity, wind speed/direction, and precipitation intensity. We are also installing about (40) autonomous soil temperature profile kits adjacent to northern stations. While the priority continues to be collecting seismic data, these additional strong motion, atmospheric, and soil temperature sensors may motivate the desire extend the operation of certain stations in cooperation with these organizations. The TA has always been amenable to partnerships in the research and education communities that extend the capabilities and reach of the EarthScope Transportable Array.

The Emerging Legacy of USArray: New Views of the Architecture of the North American Continent

NASA Astrophysics Data System (ADS)

Ritzwoller, M. H.

2013-12-01

In the decade that preceded the new millennium, seismologists on several continents dared to think big: envisioning, designing, and then building seismic arrays of unprecedented quality, resolution, and scale. In the US, their vision became USArray: thousands of broadband seismometers spanning the continent, professionally deployed, superbly maintained, with data ready in realtime quite literally at one's fingertips. For many young (and not so young) seismologists the building of USArray, particularly the Transportable Array, marks the crucial event of their scientific careers. An important part of the legacy of USArray will be an improved understanding of the architecture of the North American continent - one of its seminal motivations. A more dimly perceived motivation, but perhaps more important aspect of its legacy, will be its impact on the discipline of seismology. The impacts are profound and broad, but I will speak only about one small area: the transformation of array-based surface wave seismology. Innovations stimulated by USArray include the creation of ambient noise tomography, the reformulation of the tomographic inverse problem in terms of local differential filters applied to observed travel time and amplitude fields, the extrication of subtle signals that reveal robust and independent information about anisotropy in the crust and mantle, and the joint interpretation with other kinds of geophysical data. Interpreting the results of these innovations in a Bayesian framework helps to define another legacy of USArray, the replacement of single models with statistical distributions of model variables that can be assimilated by researchers in other fields or by seismologists in the future. As we transition to considering the scientific legacy of USArray, it is important to remember Beno Gutenberg's faith in the power of data to resolve scientific dispute. As he stated in the next to last sentence of his remarkable book Physics of the Earth's Interior: "THE DATA MUST BE GREATLY AMPLIFIED AND STRENGTHENED" (Gutenberg's emphasis). Upcoming generations of seismologists will be well served to heed Gutenberg's advice and follow the example of the designers of USArray.

Studies Of Infrasonic Propagation Using Dense Seismic Networks

NASA Astrophysics Data System (ADS)

Hedlin, M. A.; deGroot-Hedlin, C. D.; Drob, D. P.

2011-12-01

Although there are approximately 100 infrasonic arrays worldwide, more than ever before, the station density is still insufficient to provide validation for detailed propagation modeling. Relatively large infrasonic signals can be observed on seismic channels due to coupling at the Earth's surface. Recent research, using data from the 70-km spaced 400-station USArray and other seismic network deployments, has shown the value of dense seismic network data for filling in the gaps between infrasonic arrays. The dense sampling of the infrasonic wavefield has allowed us to observe complete travel-time branches of infrasound and address important research problems in infrasonic propagation. We present our analysis of infrasound created by a series of rocket motor detonations that occurred at the UTTR facility in Utah in 2007. These data were well recorded by the USArray seismometers. We use the precisely located blasts to assess the utility of G2S mesoscale models and methods to synthesize infrasonic propagation. We model the travel times of the branches using a ray-based approach and the complete wavefield using a FDTD algorithm. Although results from both rays and FDTD approaches predict the travel times to within several seconds, only about 40% of signals are predicted using rays largely due to penetration of sound into shadow zones. FDTD predicts some sound penetration into the shadow zone, but the observed shadow zones, as defined by the seismic data, have considerably narrower spatial extent than either method predicts, perhaps due to un-modeled small-scale structure in the atmosphere.

EarthScope's Plate Boundary Observatory in Alaska: Building on Existing Infrastructure to Provide a Platform for Integrated Research and Hazard-monitoring Efforts

NASA Astrophysics Data System (ADS)

Boyce, E. S.; Bierma, R. M.; Willoughby, H.; Feaux, K.; Mattioli, G. S.; Enders, M.; Busby, R. W.

2014-12-01

EarthScope's geodetic component in Alaska, the UNAVCO-operated Plate Boundary Observatory (PBO) network, includes 139 continuous GPS sites and 41 supporting telemetry relays. These are spread across a vast area, from northern AK to the Aleutians. Forty-five of these stations were installed or have been upgraded in cooperation with various partner agencies and currently provide data collection and transmission for more than one group. Leveraging existing infrastructure normally has multiple benefits, such as easier permitting requirements and costs savings through reduced overall construction and maintenance expenses. At some sites, PBO-AK power and communications systems have additional capacity beyond that which is needed for reliable acquisition of GPS data. Where permits allow, such stations could serve as platforms for additional instrumentation or real-time observing needs. With the expansion of the Transportable Array (TA) into Alaska, there is increased interest to leverage existing EarthScope resources for station co-location and telemetry integration. Because of the complexity and difficulty of long-term O&M at PBO sites, however, actual integration of GPS and seismic equipment must be considered on a case-by-case basis. UNAVCO currently operates two integrated GPS/seismic stations in collaboration with the Alaska Earthquake Center, and three with the Alaska Volcano Observatory. By the end of 2014, PBO and TA plan to install another four integrated and/or co-located geodetic and seismic systems. While three of these are designed around existing PBO stations, one will be a completely new TA installation, providing PBO with an opportunity to expand geodetic data collection in Alaska within the limited operations and maintenance phase of the project. We will present some of the design considerations, outcomes, and lessons learned from past and ongoing projects to integrate seismometers and other instrumentation at PBO-Alaska stations. Developing the PBO network as a platform for ongoing research and hazard monitoring equipment may also continue to serve the needs of the research community and the public beyond the sun-setting and completion of EarthScope science plan in 2018.

Using EarthScope Construction of the Plate Boundary Observatory to Provide Locally Based Experiential Education and Outreach

NASA Astrophysics Data System (ADS)

Jackson, M.; Eriksson, S.; Barbour, K.; Venator, S.; Mencin, D.; Prescott, W.

2006-12-01

EarthScope is an NSF-funded, national science initiative to explore the structure and evolution of the North American continent and to understand the physical processes controlling earthquakes and volcanoes. This large-scale experiment provides locally based opportunities for education and outreach which engage students at various levels and the public. UNAVCO is responsible for the Plate Boundary Observatory (PBO) component of EarthScope. PBO includes the installation and operations and maintenance of large networks of Global Positioning Satellite (GPS), strainmeter, seismometer, and tiltmeter instruments and the acquisition of satellite radar imagery, all of which will be used to measure and map the smallest movements across faults, the magma movement inside active volcanoes and the very wide areas of deformation associated with plate tectonic motion. UNAVCO, through its own education and outreach activities and in collaboration with the EarthScope E&O Program, uses the PBO construction activities to increase the understanding and public appreciation of geodynamics, earth deformation processes, and their relevance to society. These include programs for public outreach via various media, events associated with local installations, a program to employ students in the construction of PBO, and development of curricular materials by use in local schools associated with the EarthScope geographic areas of focus. PBO provides information to the media to serve the needs of various groups and localities, including interpretive centers at national parks and forests, such as Mt. St. Helens. UNAVCO staff contributed to a television special with the Spanish language network Univision Aquí y Ahora program focused on the San Andreas Fault and volcanoes in Alaska. PBO participated in an Education Day at the Pathfinder Ranch Science and Outdoor Education School in Mountain Center, California. Pathfinder Ranch hosts two of the eight EarthScope borehole strainmeters in the Anza region to study the area between the San Andreas Fault and the San Jacinto Fault. The event provided an opportunity for the Pathfinder Ranch to unveil the instruments and describe the important science behind the project to the school's students, staff, and board members. The two strainmeters will be used as a teaching tool for several years as hundreds of students filter through Pathfinder school. UNAVCO sponsors a summer PBO Student Field Assistant Program designed to give students from a variety of educational backgrounds the opportunity get involved in the construction of the EarthScope PBO project. The goal of the program is to excite students about the geodetic sciences through direct work experience. Over the summers of 2005 and 2006, PBO sponsored a total of 11 student assistants who helped to install GPS and strainmeter stations and to perform operations and maintenance tasks. PBO plans to expand this program in 2007 by including student assistants in our data management and strainmeter data processing activities. In August, 2006, UNAVCO led a group of scientists, teachers, and curriculum developers to identify key scientific concepts of EarthScope research and how they can be translated into the Earth Science classroom at the middle and high school levels. The focus was on the Cascadia region. A feature of the workshop was to use PBO and USArray data in the classroom.

Thirty Years Supporting Portable Arrays: The IRIS Passcal Instrument Center

NASA Astrophysics Data System (ADS)

Beaudoin, B. C.; Anderson, K. R.; Bilek, S. L.; Woodward, R.

2014-12-01

Thirty years have passed since establishment of the IRIS Program for the Array Seismic Studies of the Continental Lithosphere (PASSCAL). PASSCAL was part of a coordinated plan proposed to the National Science Foundation (NSF) defining the instrumentation, data collection and management structure to support a wide range of research in seismology. The PASSCAL program has surpassed the early goal of 6000 data acquisition channels with a current inventory of instrumentation capable of imaging from the near surface to the inner core. Here we present the evolution of the PASSCAL program from instrument depot to full service community resource. PASSCAL has supported close to 1100 PI driven seismic experiments since its inception. Instruments from PASSCAL have covered the globe and have contributed over 7400 SEED stations and 242 assembled data sets to the IRIS Data Management Center in Seattle. Since the combination in 1998 of the Stanford and Lamont instrument centers into the single PASSCAL Instrument Center (PIC) at New Mexico Tech, the facility has grown in scope by adding the EarthScope Array Operations Facility in 2005, the incorporation of the EarthScope Flexible Array, and a Polar support group in 2006. The polar support group enhances portable seismic experiments in extremely harsh polar environments and also extends to special projects such as the Greenland Ice Sheet Monitoring Network (GLISN) and the recent development effort for Geophysical Earth Observatory for Ice Covered Environments (GEOICE). Through these support efforts the PIC has established itself as a resource for field practices, engineered solutions for autonomous seismic stations, and a pioneer in successful seismic recording in polar environments. We are on the cusp of a new generation of instrumentation driven in part by the academic community's desire to record unaliased wavefields in multiple frequency bands and industry's interest in utilizing lower frequency data. As part of the recently funded IRIS proposal to NSF for support of Seismological Facilities for the Advancement of Geoscience and EarthScope (SAGE), IRIS is developing plans for this new instrumentation that will ensure that the PASSCAL program continues to provide state-of-the-art observing capabilities into the coming decades.

Epicenter Location of Regional Seismic Events Using Love Wave and Rayleigh Wave Ambient Seismic Noise Green's Functions

NASA Astrophysics Data System (ADS)

Levshin, A. L.; Barmin, M. P.; Moschetti, M. P.; Mendoza, C.; Ritzwoller, M. H.

2011-12-01

We describe a novel method to locate regional seismic events based on exploiting Empirical Green's Functions (EGF) that are produced from ambient seismic noise. Elastic EGFs between pairs of seismic stations are determined by cross-correlating long time-series of ambient noise recorded at the two stations. The EGFs principally contain Rayleigh waves on the vertical-vertical cross-correlations and Love waves on the transverse-transverse cross-correlations. Earlier work (Barmin et al., "Epicentral location based on Rayleigh wave empirical Green's functions from ambient seismic noise", Geophys. J. Int., 2011) showed that group time delays observed on Rayleigh wave EGFs can be exploited to locate to within about 1 km moderate sized earthquakes using USArray Transportable Array (TA) stations. The principal advantage of the method is that the ambient noise EGFs are affected by lateral variations in structure similarly to the earthquake signals, so the location is largely unbiased by 3-D structure. However, locations based on Rayleigh waves alone may be biased by more than 1 km if the earthquake depth is unknown but lies between 2 km and 7 km. This presentation is motivated by the fact that group time delays for Love waves are much less affected by earthquake depth than Rayleigh waves; thus exploitation of Love wave EGFs may reduce location bias caused by uncertainty in event depth. The advantage of Love waves to locate seismic events, however, is mitigated by the fact that Love wave EGFs have a smaller SNR than Rayleigh waves. Here, we test the use of Love and Rayleigh wave EGFs between 5- and 15-sec period to locate seismic events based on the USArray TA in the western US. We focus on locating aftershocks of the 2008 M 6.0 Wells earthquake, mining blasts in Wyoming and Montana, and small earthquakes near Norman, OK and Dallas, TX, some of which may be triggered by hydrofracking or injection wells.

The Denali EarthScope Education Partnership: Creating Opportunities for Learning About Solid Earth Processes in Alaska and Beyond.

NASA Astrophysics Data System (ADS)

Roush, J. J.; Hansen, R. A.

2003-12-01

The Geophysical Institute of the University of Alaska Fairbanks, in partnership with Denali National Park and Preserve, has begun an education outreach program that will create learning opportunities in solid earth geophysics for a wide sector of the public. We will capitalize upon a unique coincidence of heightened public interest in earthquakes (due to the M 7.9 Denali Fault event of Nov. 3rd, 2002), the startup of the EarthScope experiment, and the construction of the Denali Science & Learning Center, a premiere facility for science education located just 43 miles from the epicenter of the Denali Fault earthquake. Real-time data and current research results from EarthScope installations and science projects in Alaska will be used to engage students and teachers, national park visitors, and the general public in a discovery process that will enhance public understanding of tectonics, seismicity and volcanism along the boundary between the Pacific and North American plates. Activities will take place in five program areas, which are: 1) museum displays and exhibits, 2) outreach via print publications and electronic media, 3) curriculum development to enhance K-12 earth science education, 4) teacher training to develop earth science expertise among K-12 educators, and 5) interaction between scientists and the public. In order to engage the over 1 million annual visitors to Denali, as well as people throughout Alaska, project activities will correspond with the opening of the Denali Science and Learning Center in 2004. An electronic interactive kiosk is being constructed to provide public access to real-time data from seismic and geodetic monitoring networks in Alaska, as well as cutting edge visualizations of solid earth processes. A series of print publications and a website providing access to real-time seismic and geodetic data will be developed for park visitors and the general public, highlighting EarthScope science in Alaska. A suite of curriculum modules will be developed for middle school classrooms to enrich earth science curricula by taking students into the field, and by providing opportunities to interact with scientists using real EarthScope data and research results. Curriculum modules will take advantage of Denali's new "Nature Area Network", an IEEE 802.11b wireless network serving the backcountry areas of the Park where students can engage in hands on learning about geology and geophysics and share their experiences with students worldwide via the Internet. Curricula will also focus on the new field of digital story telling, in which students will develop their own understanding of solid earth processes by creating digital stories using readily available digital moviemaking technology. A training course will be developed to enhance K-12 educators' ability to teach earth science utilizing real data and research results. And a series of public lectures both at Denali and in communities across Alaska will engage Geophysical Institute researchers with the public and foster wider participation in the EarthScope Experiment. The anticipated benefits of this project are many. An increase in public awareness and understanding of solid earth processes will lead to better preparedness, and improved decision making regarding the mitigation of risk from seismic and volcanic hazards. Earth science education will be made more vital and engaging for both students and teachers. And Alaska's visitors and residents will gain a better understand and greater appreciation for the dynamic tectonic processes that have created the rugged landscape of the state and its national parklands.

Modeling the Excitation of Seismic Waves by the Joplin Tornado

NASA Astrophysics Data System (ADS)

Valovcin, Anne; Tanimoto, Toshiro

2017-10-01

Tornadoes generate seismic signals when they contact the ground. Here we examine the signals excited by the Joplin tornado, which passed within 2 km of a station in the Earthscope Transportable Array. We model the tornado-generated vertical seismic signal at low frequencies (0.01-0.03 Hz) and solve for the strength of the seismic source. The resulting source amplitude is largest when the tornado was reported to be strongest (EF 4-5), and the amplitude is smallest when the tornado was weak (EF 0-2). A further understanding of the relationship between source amplitude and tornado intensity could open up new ways to study tornadoes from the ground.

Imaging Strong Lateral Heterogeneities with USArray using Body-to-Surface Wave Scattering

NASA Astrophysics Data System (ADS)

Yu, C.; Zhan, Z.; Hauksson, E.; Cochran, E. S.

2017-12-01

Seismic scattering is commonly observed and results from wave propagation in heterogeneous medium. Yet, deterministic characterization of scatterers remains challenging. In this study, we analyze broadband waveforms recorded by the USArray across the entire conterminous US. With array analysis, we observe strong scattered surface waves following the arrival of teleseismic body waves over several hundreds of kilometers. We use back-projection to locate the body-to-surface scattering sources, and detect strong scatterers both around and within the conterminous US. For the former, strong scattering is associated with pronounced bathymetric relief, such as the Patton Escarpment in the Southern California Continental Borderland. For the latter, scatterers are consistent with sharp lateral heterogeneities, such as near the Yellowstone hotspot and Southern California fault zones. We further model the body-to-surface wave scattering using finite-difference simulations. As an example, in the Southern California Continental Borderland a simplified 2-D bathymetric and crustal model are able to predict the arrival times and amplitudes of major scatterers. The modeling also suggests a relatively low shear wave velocity in the Continental Borderland. These observation of strong body-to-surface wave scattering and waveform modeling not only helps us image sharp heterogeneities but also are useful for assessing seismic hazard, including the calibration and refinement of seismic velocity models used to locate earthquakes and simulate strong ground motions.

In-Situ Lithospheric Rheology Measurement Using Isostatic Response and Geophysical State

NASA Astrophysics Data System (ADS)

Lowry, A. R.; Becker, T. W.; Buehler, J. S.; ma, X.; Miller, M. S.; Perez-Gussinye, M.; Ravat, D.; Schutt, D.

2013-12-01

Measurements of effective elastic thickness, Te, from flexural isostatic modeling are sensitive to flow rheology of the lithosphere. Nevertheless, Te has not been widely used to estimate in-situ rheology. Past methodological controversies regarding Te measurement are partly to blame for under-utilization of isostatic response in rheology studies, but these controversies are now largely resolved. The remaining hurdles include uncertainties in properties of geophysical state such as temperature, lithology, and water content. These are ambiguous in their relative contributions to total strength, and the unknown state-of-stress adds to ambiguity in the rheology. Dense seismic and other geophysical arrays such as EarthScope's USArray are providing a wealth of new information about physical state of the lithosphere, however, and these data promise new insights into rheology and deformation processes. For example, new estimates of subsurface mass distributions derived from seismic data enable us to examine controversial assumptions about the nature of lithospheric loads. Variations in crustal lithology evident in bulk crustal velocity ratio, vP/vS, contribute a surprisingly large fraction of total loading. Perhaps the most interesting new information on physical state derives from imaging of uppermost mantle velocities using refracted mantle phases, Pn and Sn, and depths to negative velocity gradients imaged as converted phases in receiver functions (so-called seismic lithosphere-asthenosphere boundary, 'LAB', and mid-lithosphere discontinuity, 'MLD'). Imaging of the ~580°C isotherm associated with the phase transition from alpha- to beta-quartz affords another exciting new avenue for investigation, in part because the transition closely matches the Curie temperature thought to control magnetic bottom in some continental crust. Reconciling seismic estimates of temperature variations with measurements of Te and upper-mantle negative velocity gradients in the US requires that we invoke variations in lithology, water concentrations, and/or membrane stress. In deforming lithosphere, Te and Pn are best-reconciled using a wet quartz crustal lithology, wet olivine mantle lithology, and large membrane stress. More stable lithosphere to the east is best-modeled with a dry feldspar or pyroxene crustal lithology and dry olivine in the mantle. Greater crustal quartz abundance in deforming lithosphere (and in ancient orogens further east) is observed independently in measurements of bulk-crustal vP/vS. Independent evidence also supports the inference of variable water concentrations. Taken together, these lines of evidence suggest that lithology and water abundance are at least as important as temperature variation in determining rheological behavior of the lithosphere.

Velocity model calibration as a tool to improve regional wave moment tensors: Application to the Basin and Range Province

NASA Astrophysics Data System (ADS)

Ichinose, G. A.

2006-12-01

Many scientific issues for the Basin and Range Province (BRP) remain unsettled including structural evolution, strain rates, slip partitioning and earthquake source physics. A catalog of earthquake source parameters including locations and moment tensors is the basis for tectonic and geophysical study. New instrumentation from the Advance National Seismic System, EarthScope Plate Boundary Observatory, Bigfoot and US-Array brings the opportunity for high quality research; therefore, a catalog is an underlying foundation for examining the BRP. We are continuing to generate a moment tensor catalog for the BRP (Mw<3.5) using long-period regional waves spanning back to 1990. Iterative waveform inversion method (e.g., Nolet et al., 1986, Randell, 1994) is used to calibrate the BRP velocity and density structure using two northern and southern BRP earthquakes. The calibrated models generate realistic synthetics for (f<0.5Hz) with ~50-80% variance reduction. We averaged all path specific models to construct a 1-D BRP community background model. The crust is relatively simple between 5-20km (~6.12km/s) and there is a strong velocity gradient in the upper 5- km. There are lower velocities in the upper crust but higher velocities in the mid-crust for the Sierra Nevada paths relative to BRP. There is also a lower crust high-velocity anomaly near Battle Mountain and Elko that is faster by ~5% and may indicate a wider area of under-plating by basaltic magmas. There are significant low velocity zones in the upper and mid crust mainly across the Walker Lane Belt that may indicate the presence of fluids. We are continuing to work on assessing the performance of these newly calibrated models in improving the estimation of moment tensors down to lower magnitudes and mapping out holes in the seismic network which can be filled to improve moment tensor catalog. We also are looking at how these models work at locating earthquakes and comparing synthetics with those computed from models constrained from different data including refraction, surface wave dispersion, and travel-time tomography.

Teleseismic P-wave Delay Time Tomography of the southern Superior Province and Midcontinent Rift System (MRS) Region

NASA Astrophysics Data System (ADS)

Bollmann, T. A.; van der Lee, S.; Frederiksen, A. W.; Wolin, E.; Aleqabi, G. I.; Revenaugh, J.; Wiens, D. A.; Darbyshire, F. A.

2014-12-01

The Superior Province Rifting Earthscope Experiment (SPREE) and the northern midwest footprint of USArray's Transportable Array recorded continuous ground motion for a period of 2.5 years. From around 400 M>5.5 teleseismic earthquakes recorded at 337 stations, we measured body wave delay times for 255 of these earthquakes. The P wave delays are accumulated over more than 45 thousand wave paths with turning points in the lower mantle. We combine these delay times with a similar number delay times used in previous tomographic studies of the study region. The latter delay times stem from fewer stations, including Polaris and CNSN stations, and nearly a thousand earthquakes. We combine these two sets of delay times to image the three-dimensional distribution of seismic velocity variations beneath the southern Superior Province and surrounding provinces. This combined data coverage is illustrated in the accompanying figure for a total number of 447 stations . The coverage and the combined delays form the best configuration yet to image the three-dimensional distribution of seismic P and S-wave velocity variations beneath the southern Superior and surrounding provinces. Closely spaced stations (~12 km) along and across the MRS provide higher resolving power for lithospheric structure beneath the rift system. Conforming to expectations that the entire region is underlain by thick, cool lithosphere, a mean delay of -.55 +/- .54 s. This is very similar to the mean delays -.6s +/- .37s measured for this region before 2012. Event corrections range from -.2 +/-.54 s and correlate with tectonics for 80% of the earthquakes. An inversion of these nearly one hundred thousand P and around thirty thousand S-wave delay times for high-resolution P and S-wave velocity structure, respectively, does not show structures that are obviously related to the crustal signature of the MRS. None of structures imaged, align with or have a similar shape to the high Mid-continent Gravity Anomaly (MGA). However, a low-velocity structure is imaged in the lithosphere just east of the MGA.

Accessing SAFOD data products: Downhole measurements, physical samples and long-term monitoring

NASA Astrophysics Data System (ADS)

Weiland, C.; Zoback, M.; Hickman, S. H.; Ellsworth, W. L.

2005-12-01

Many different types of data were collected during SAFOD Phases 1 and 2 (2004-2005) as part of the National Science Foundation's EarthScope program as well as from the SAFOD Pilot Hole, drilled in 2002 and funded by the International Continental Drilling Program (ICDP). Both SAFOD and the SAFOD Pilot Hole are being conducted as a close collaboration between NSF, the U.S. Geological Survey and the ICDP. SAFOD data products include cuttings, core and fluid samples; borehole geophysical measurements; and strain, tilt, and seismic recordings from the multilevel SAFOD borehole monitoring instruments. As with all elements of EarthScope, these data (and samples) are openly available to members of the scientific and educational communities. This paper presents the acquisition, storage and distribution plan for SAFOD data products. Washed and unwashed drill cuttings and mud samples were collected during Phases 1 and 2, along with three spot cores at depths of 1.5, 2.5, and 3.1 km. A total of 52 side-wall cores were also collected in the open-hole interval between 2.5 and 3.1 km depth. The primary coring effort will occur during Phase 3 (2007), when we will continuously core up to four, 250-m-long multilaterals directly within and adjacent to the San Andreas Fault Zone. Drill cuttings, core, and fluid samples from all three Phases of SAFOD drilling are being curated under carefully controlled conditions at the Integrated Ocean Drilling Program (IODP) Gulf Coast Repository in College Station, Texas. Photos of all physical samples and a downloadable sample request form are available on the ICDP website (http://www.icdp-online.de/sites/sanandreas/index/index.html). A suite of downhole geophysical measurements was conducted during the first two Phases of SAFOD drilling, as well as during drilling of the SAFOD Pilot Hole. These data include density, resistivity, porosity, seismic and borehole image logs and are also available via the ICDP website. The SAFOD monitoring program includes fiber-optic strain, tilt, seismic and fluid-pressure recording instruments. Seismic data from the Pilot Hole array are now available in SEED format from the Northern California Earthquake Data Center (http://quake.geo.berkeley.edu/safod/). The strain and tilt instruments are still undergoing testing and quality assurance, and these data will be available through the same web site as soon as possible. Lastly, two terabytes of unprocessed (SEG-2 format) data from a two-week deployment of an 80-level seismic array during April/May 2005 by Paulsson Geophysical Services, Inc. are now available via the IRIS data center (http://www.iris.edu/data/data.htm). Drilling parameters include real-time descriptions of drill cuttings mineralogy, drilling mud properties, and mechanical data related to the drilling process and are available via the ICDP web site. Current status reports on SAFOD drilling, borehole measurements, sampling, and monitoring instrumentation will continue to be available from the EarthScope web site (http://www.earthscope.org).

EarthScope Transportable Array Siting Outreach Activities in Alaska and Western Canada

NASA Astrophysics Data System (ADS)

Dorr, P. M.; Gardine, L.; Tape, C.; McQuillan, P.; Cubley, J. F.; Samolczyk, M. A.; Taber, J.; West, M. E.; Busby, R.

2015-12-01

The EarthScope Transportable Array is deploying about 260 stations in Alaska and western Canada. IRIS and EarthScope are partnering with the Alaska Earthquake Center, part of the University of Alaska's Geophysical Institute, and Yukon College to spread awareness of earthquakes in Alaska and western Canada and the benefits of the Transportable Array for people living in these regions. We provide an update of ongoing education and outreach activities in Alaska and Canada as well as continued efforts to publicize the Transportable Array in the Lower 48. Nearly all parts of Alaska and portions of western Canada are tectonically active. The tectonic and seismic variability of Alaska, in particular, requires focused attention at the regional level, and the remoteness and inaccessibility of most Alaskan and western Canadian villages and towns often makes frequent visits difficult. When a community is accessible, every opportunity to engage the residents is made. Booths at state fairs and large cultural gatherings, such as the annual convention of the Alaska Federation of Natives, are excellent venues to distribute earthquake information and to demonstrate a wide variety of educational products and web-based applications related to seismology and the Transportable Array that residents can use in their own communities. Meetings and interviews with Alaska Native Elders and tribal councils discussing past earthquakes has led to a better understanding of how Alaskans view and understand earthquakes. Region-specific publications have been developed to tie in a sense of place for residents of Alaska and the Yukon. The Alaska content for IRIS's Active Earth Monitor emphasizes the widespread tectonic and seismic features and offers not just Alaska residents, but anyone interested in Alaska, a glimpse into what is going on beneath their feet. The concerted efforts of the outreach team will have lasting effects on Alaskan and Canadian understanding of the seismic hazard and tectonics of the region.

EarthScope Transportable Array Siting Outreach Activities in Alaska and Western Canada

NASA Astrophysics Data System (ADS)

Gardine, L.; Dorr, P. M.; Tape, C.; McQuillan, P.; Taber, J.; West, M. E.; Busby, R. W.

2014-12-01

The EarthScopeTransportable Array is working to locate over 260 stations in Alaska and western Canada. In this region, new tactics and partnerships are needed to increase outreach exposure. IRIS and EarthScope are partnering with the Alaska Earthquake Center, part of University of Alaska Geophysical Institute, to spread awareness of Alaska earthquakes and the benefits of the Transportable Array for Alaskans. Nearly all parts of Alaska are tectonically active. The tectonic and seismic variability of Alaska requires focused attention at the regional level, and the remoteness and inaccessibility of most Alaska villages and towns often makes frequent visits difficult. For this reason, Alaska outreach most often occurs at community events. When a community is accessible, every opportunity to engage the residents is made. Booths at state fairs and large cultural gatherings, such as the annual convention of the Alaska Federation of Natives, are excellent venues to distribute earthquake information and to demonstrate a wide variety of educational products and web-based applications related to seismology and the Transportable Array that residents can use in their own communities. Region-specific publications have been developed to tie in a sense of place for residents of Alaska. The Alaska content for IRIS's Active Earth Monitor will emphasize the widespread tectonic and seismic features and offer not just Alaska residents, but anyone interested in Alaska, a glimpse into what is going on beneath their feet. The concerted efforts of the outreach team will have lasting effects on Alaskan understanding of the seismic hazard and tectonics of the region. Efforts to publicize the presence of the Transportable Array in Alaska, western Canada, and the Lower 48 also continue. There have been recent articles published in university, local and regional newspapers; stories appearing in national and international print and broadcast media; and documentaries produced by some of the world's most respected scientific and educational production companies that have included a segment about EarthScope and the Transportable Array.

Moving Closer to EarthScope: A Major New Initiative for the Earth Sciences*

NASA Astrophysics Data System (ADS)

Simpson, D.; Blewitt, G.; Ekstrom, G.; Henyey, T.; Hickman, S.; Prescott, W.; Zoback, M.

2002-12-01

EarthScope is a scientific research and infrastructure initiative designed to provide a suite of new observational facilities to address fundamental questions about the evolution of continents and the processes responsible for earthquakes and volcanic eruptions. The integrated observing systems that will comprise EarthScope capitalize on recent developments in sensor technology and communications to provide Earth scientists with synoptic and high-resolution data derived from a variety of geophysical sensors. An array of 400 broadband seismometers will spend more than ten years crossing the contiguous 48 states and Alaska to image features that make up the internal structure of the continent and underlying mantle. Additional seismic and electromagnetic instrumentation will be available for high resolution imaging of geological targets of special interest. A network of continuously recording Global Positioning System (GPS) receivers and sensitive borehole strainmeters will be installed along the western U.S. plate boundary. These sensors will measure how western North America is deforming, what motions occur along faults, how earthquakes start, and how magma flows beneath active volcanoes. A four-kilometer deep observatory bored directly into the San Andreas fault will provide the first opportunity to observe directly the conditions under which earthquakes occur, to collect fault rocks and fluids for laboratory study, and to monitor continuously an active fault zone at depth. All data from the EarthScope facilities will be openly available in real-time to maximize participation from the scientific community and to provide on-going educational outreach to students and the public. EarthScope's sensors will revolutionize observational Earth science in terms of the quantity, quality and spatial extent of the data they provide. Turning these data into exciting scientific discovery will require new modes of experimentation and interdisciplinary cooperation from the Earth science community. A broad sector of the university research community has joined with federal agencies to stimulate the development of facility plans and move EarthScope forward as a coordinated national initiative. With strong prospects for funding next year, the time is right for bold new ideas on how to maximize the use of these powerful new resources in the Earth scientist's toolkit. * On behalf of the EarthScope Working Group

Amplification and Attenuation Across USArray Using Ambient Noise Wavefront Tracking

NASA Astrophysics Data System (ADS)

Bowden, Daniel C.; Tsai, Victor C.; Lin, Fan-Chi

2017-12-01

As seismic traveltime tomography continues to be refined using data from the vast USArray data set, it is advantageous to also exploit the amplitude information carried by seismic waves. We use ambient noise cross correlation to make observations of surface wave amplification and attenuation at shorter periods (8-32 s) than can be observed with only traditional teleseismic earthquake sources. We show that the wavefront tracking approach can be successfully applied to ambient noise correlations, yielding results quite similar to those from earthquake observations at periods of overlap. This consistency indicates that the wavefront tracking approach is viable for use with ambient noise correlations, despite concerns of the inhomogeneous and unknown distribution of noise sources. The resulting amplification and attenuation maps correlate well with known tectonic and crustal structure; at the shortest periods, our amplification and attenuation maps correlate well with surface geology and known sedimentary basins, while our longest period amplitudes are controlled by crustal thickness and begin to probe upper mantle materials. These amplification and attenuation observations are sensitive to crustal materials in different ways than traveltime observations and may be used to better constrain temperature or density variations. We also value them as an independent means of describing the lateral variability of observed Rayleigh wave amplitudes without the need for 3-D tomographic inversions.

Imaging Subduction, Episodic Tremor and Slip in the Pacific Northwest: Cascadia Arrays For Earthscope (CAFE)

NASA Astrophysics Data System (ADS)

Abers, G. A.; Rondenay, S.; Creager, K. C.; Malone, S. D.; Zhang, Z.; Wech, A. G.; Sweet, J. R.; Melbourne, T. I.; Hacker, B. R.

2007-12-01

Subduction delivers fluids into the Earth's mantle by transport of hydrated crust downward in subducting plates. These fluids are released at depth and may be responsible for a wide variety of phenomena including weakened thrust faults, episodic tremor and slip (ETS), intraslab earthquakes, forearc serpentinization, and arc magmatism. Cascadia is the volcanic arc associated with the youngest subducting plate, and hence a primary EarthScope target. In 2006 we launched Cascadia Arrays For Earthscope (CAFE), an EarthScope effort utilizing Flexible Array, Transportable Array, and PBO facilities, and integrating these data with complementary constraints from geodynamics and geochemistry. Seismic imaging, the emphasis of this presentation, is employed to illuminate (i) the descending oceanic plate, from where fluids are expelled by metamorphism, and (ii) the mantle wedge, where fluids migrate to produce hydrous phases such as serpentine or, beneath the volcanic arc, primary magmas, and (iii) the interface between them where ETS may be produced. The experiment traverses a section of the Cascadia system where earthquakes extend to nearly 100 km depth, thus permitting an investigation of the relationship between the release of fluids and the generation of Wadati-Benioff-zone earthquakes, and crosses regions of ETS excitation. The basic experiment has four components: (1) a 47-element broadband imaging array of Flexible Array instruments integrated with Bigfoot; (2) three small-aperture seismic arrays with 15 additional short-period instruments near known sources of ETS; (3) analysis of the PBO and PANGA GPS data sets to define the details of episodic slip events; and (4) integrative modeling. Sixty-two seismographs were deployed in July 2006; here we present a first look at the experiment and the data collected. Initial data recovery has been excellent, with approximately 12 months of continuous data recovered as of this writing, most delivered to the IRIS DMC. This time window includes an ETS episode in Jan. 2007. Given the success of this deployment, we expect to make good progress toward understanding the relationship between subduction, ETS, and fluid cycling.

A tree fell in the forest, and SPREE heard it: seismic recording of the 2011 St. Croix Valley Blowdown

NASA Astrophysics Data System (ADS)

Wolin, E.; van der Lee, S.

2016-12-01

As part of the Superior Province Rifting Earthscope Experiment (SPREE), 82 broadband seismic stations from the EarthScope Flexible Array pool were deployed by the SPREE team from April 2011 through October 2013, to explore the deep structure of the Mid-Continent Rift System (Stein et al., 2011). The deployment included two crosslines with approximate station spacing of 10 km centered near the northern Minnesota-Wisconsin border. Analysis of long-period noise reveals strong seasonal and diurnal variations (Wolin et al., 2015). On 1 July 2011, a severe thunderstorm system swept over the St. Croix Valley, passing directly over the dense SPREE array. This storm system was accompanied by a series of downbursts that generated straight-line winds in excess of 100 km/hr, resulting in extensive damage to hundreds of thousands of acres of forest. Seven SPREE stations were located in the path of the storm, with two stations in the center of areas that were heavily damaged by downbursts. The stations remained in operation throughout this extreme weather event, capturing a unique record of ground noise generated by the storm system. We compare available radar reflectivity data with seismic noise power spectra throughout the event and show that storm cells generated significant broadband seismic signals as they passed over the region. Relative to typical background seismic noise levels, power between 0.05-10 Hz increased by 5-20 dB during the storm. Seismic noise levels can be compared to available wind speed data to provide a detailed record of wind speeds during the weather event. We also explore the long-period coherence of energy across the array, which is potentially useful to help constrain near-surface velocity structure at the array sites as well as to better characterize how atmospheric processes couple into the solid earth during severe weather events.

Tracking the Progress of EarthScope/USArray: The crust and upper mantle beneath the transition region between tectonic western US and cratonic eastern US

NASA Astrophysics Data System (ADS)

Shen, W.; Lin, F.; Ritzwoller, M. H.

2010-12-01

The transition region between the tectonic western US and the cratonic eastern US contains numerous significant geological regions (e.g., the Rocky Mountains, the Colorado Plateau, and the Rio Grande Rift), and also, unknowns (e.g, the location or extent of the east-west US dichotomy, the compensation of the high topography of the western Great Plains, the extensional mechanics of the Rio Grande Rift, and the structure of the mantle beneath the Colorado Plateau). The answers to these questions and others are critical to an understanding of the tectonics and tectonic history of this region and its impact on the cratonic eastern US. The recent deployments of seismic stations, particularly the EarthScope USArray Transportable Array (TA), provide an opportunity to construct a detailed 3-D structural model of the crust and upper mantle beneath this transition region, and thus allow us to address some of the questions listed above. We present results from ambient noise tomography (ANT) and teleseismic earthquake tomography by using data from TA stations within the western and central US. We processed continuous seismic noise data from ~600 TA stations from August 2008 to March 2010, which after data selection produces a data set with ~100,000 inter-station paths. Rayleigh wave phase speed maps between 6 and 40 sec period and Love wave phase speed maps between 8 and 30 sec with a resolution of ~60 km are constructed using eikonal tomography. In addition, we applied eikonal tomography (ET) to about 300 teleseismic earthquakes to obtain long-period (30 - 100 sec) Rayleigh wave phase speed maps and Love wave phase speeds maps (30 - 60 sec). By jointly inverting Rayleigh and Love phase speeds maps from ANT and earthquake tomography, we constructed a 3-D isotropic and radially anisotropic shear velocity model of the crust and upper mantle to ~150 km depth together with model uncertainties constrained by a Monte-Carlo inversion. The 3-D isotropic model reveals a variety of robust features in this transition region. In the uppermost crust, the main sedimentary basins (e.g., Green River, Uinta, Washakie, Powder River, Denver, Albuquerque, Permian, and Anadarko) are imaged. In the middle and lower crust where the low shear velocities from basins diminish, the Yellowstone hot spot becomes the main slow anomaly. In the uppermost mantle, high velocity anomalies are observed beneath the Colorado Plateau, the Wyoming craton, and the Great Plains. Although the Colorado Plateau shows more or less homogeneous shear velocity in its middle and towards its northern boundary, the other two main fast anomalies reveal inhomogeneous structures at depths deeper than 100 km. Two main low velocity anomalies are observed: one underlying the Snake River Plain which broadens and dips to the northeast and another U-shaped anomaly on the eastern margin of the Colorado Plateau. These velocity anomalies add to complexities at the transition between the tectonic western US and the stable eastern US. The location and uncertainty of the east-west shear velocity dichotomy also is constrained by this model.

Source Biases in Magnetotelluric Transfer Functions due to Pc3/Pc4 ( 10-100s) Geomagnetic Activity at Mid-Latitudes

NASA Astrophysics Data System (ADS)

Murphy, B. S.; Egbert, G. D.

2017-12-01

Discussion of possible bias in magnetotelluric (MT) transfer functions due to the finite spatial scale of external source fields has largely focused on long periods (>1000 s), where skin depths are large, and high latitudes (>60° N), where sources are dominated by narrow electrojets. However, a significant fraction ( 15%) of the 1000 EarthScope USArray apparent resistivity and phase curves exhibit nonphysical "humps" over a narrow period range (typically between 25-60 s) that are suggestive of narrow-band source effects. Maps of locations in the US where these biases are seen support this conclusion: they mostly occur in places where the Earth is highly resistive, such as cratonic regions, where skin depths are largest and hence where susceptibility to bias from short-wavelength sources would be greatest. We have analyzed EarthScope MT time series using cross-phase techniques developed in the space physics community to measure the period of local field line resonances associated with geomagnetic pulsations (Pc's). In most cases the biases occur near the periods of field line resonance determined from this analysis, suggesting that at mid-latitude ( 30°-50° N) Pc's can bias the time-averaged MT transfer functions. Because Pc's have short meridional wavelengths (hundreds of km), even at these relatively short periods the plane-wave assumption of the MT technique may be violated, at least in resistive domains with large skin depths. It is unclear if these biases (generally small) are problematic for MT data inversion, but their presence in the transfer functions is already a useful zeroth-order indicator of resistive regions of the Earth.

Seismic Migration Imaging of the Mantle Transition Zone Beneath Continental US with Receiver Functions

NASA Astrophysics Data System (ADS)

Zhang, H.; Schmandt, B.

2017-12-01

The mantle transition zone has been widely studied by multiple sub-fields in geosciences including seismology, mineral physics and geodynamics. Due to the relatively high water storage capacity of olivine polymorphs (wadsleyite and ringwoodite) inside the transition zone, it is proposed to be a potential geochemical water reservoir that may contain one or more ocean masses of water. However, there is an ongoing debate about the hydration level of those minerals and how it varies from place to place. Considering that dehydration melting, which may happen during mantle flow across phase transitions between hydrated olivine polymorphs, may be seismically detectable, large-scale seismic imaging of heterogeneous scattering in the transition zone can contribute to the debate. To improve our understanding of the properties of the mantle transition zone and how they relate to mantle flow across its boundaries, it is important to gain an accurate image with large spatial coverage. The accuracy is primarily limited by the density of broadband seismic data and the imaging algorithms applied to the data, while the spatial coverage is limited by the availability of wide-aperture (>500 km) seismic arrays. Thus, the emergence of the USArray seismic data set (www.usarray.org) provides a nearly ideal data source for receiver side imaging of the mantle transition zone due to its large aperture ( 4000 km) with relatively small station spacing ( 70 km), which ensures that the transition zone beneath it is well sampled by teleseismic waves. In total, more than 200,000 P to S receiver functions will be used for imaging structures in depth range of 300 km to 800 km beneath the continental US with an improved 3D Kirchhoff pre-stacking migration method. The method uses 3-D wave fronts calculated for P and S tomography models to more accurately calculate point scattering coefficients and map receiver function lag times to 3-D position. The new images will help resolve any laterally sporadic or dipping interfaces that may be present at transition zone depths. The locations of sporadic velocity decreases will be compared with mantle flow models to evaluate the possibility of dehydration melting.

Heterogeneous distribution of water in the mantle transition zone beneath United States inferred from seismic observations

NASA Astrophysics Data System (ADS)

Wang, Y.; Pavlis, G. L.; Li, M.

2017-12-01

The amount of water in the Earth's deep mantle is critical for the evolution of the solid Earth and the atmosphere. Mineral physics studies have revealed that Wadsleyite and Ringwoodite in the mantle transition zone could store several times the volume of water in the ocean. However, the water content and its distribution in the transition zone remain enigmatic due to lack of direct observations. Here we use seismic data from the full deployment of the Earthscope Transportable Array to produce 3D image of P to S scattering of the mantle transition zone beneath the United States. We compute the image volume from 141,080 pairs of high quality receiver functions defined by the Earthscope Automated Receiver Survey, reprocessed by the generalized iterative deconvolution method and imaged by the plane wave migration method. We find that the transition zone is filled with previously unrecognized small-scale heterogeneities that produce pervasive, negative polarity P to S conversions. Seismic synthetic modeling using a point source simulation method suggests two possible structures for these objects: 1) a set of randomly distributed blobs of slight difference in size, and 2) near vertical diapir structures from small scale convections. Combining with geodynamic simulations, we interpret the observation as compositional heterogeneity from small-scale, low-velocity bodies that are water enriched. Our results indicate there is a heterogeneous distribution of water through the entire mantle transition zone beneath the contiguous United States.

Polarization Analysis of the September 2005 Northern Cascadia Episodic Tremor and Slip Event

NASA Astrophysics Data System (ADS)

Wech, A. G.; Creager, K. C.

2006-12-01

The region of Northern Cascadia, extending from the Olympic Mountains and Puget Sound to southern Vancouver Island, down-dip of the subduction "locked" zone has repeatedly experienced episodes of slow slip. This episodic slip, observed to take place over a period of two to several weeks, is accompanied by a seismic tremor signal. Based on the average recurrence interval of 14 months, the last episodic tremor and slip (ETS) event was expected to occur in September, 2005. Indeed, it began on September 3. In order to record this event, we deployed an array of 11 three-component seismometers on the northern side of the Olympic Peninsula augmenting Pacific Northwest Seismographic Network stations as well as the first few EarthScope BigFoot stations and Plate Boundary Observatory borehole seismometers. This seismic array was comprised of six short-period and five broadband instruments with average spacings of 500 m and 2200 m respectively. In conjunction with this Earthscope seismic deployment, we also installed a dense network of 29 temporary, continuous GPS stations across the entire Olympic Peninsula to integrate seismic and geodetic observations. Based on past geodetic observations, a dominant assumption for the source of tremor is fault-slip in the direction of subduction, which can be tested using polarization of the seismic tremor. Using waveform cross- correlation to invert for the direction of slowness, we observed the tremor signal to migrate directly under our array. As the source passed beneath the array, tremor polarization stabilized to coincide with the direction of subduction. During a four day period starting September 8, the normalized eigenvalue associated with the dominant linear polarization jumped from ~0.7 to a stable 0.9 value. Also during this time, the polarization azimuth stabilized to a value of 57 +/- 8 degrees, close to the angle of subduction (56 degrees) suggesting that the tremor is caused by slip in the direction of relative plate motion on one or more faults.

IRIS Arrays: Observing Wavefields at Multiple Scales and Frequencies

NASA Astrophysics Data System (ADS)

Sumy, D. F.; Woodward, R.; Frassetto, A.

2014-12-01

The Incorporated Research Institutions for Seismology (IRIS) provides instruments for creating and operating seismic arrays at a wide range of scales. As an example, for over thirty years the IRIS PASSCAL program has provided instruments to individual Principal Investigators to deploy arrays of all shapes and sizes on every continent. These arrays have ranged from just a few sensors to hundreds or even thousands of sensors, covering areas with dimensions of meters to thousands of kilometers. IRIS also operates arrays directly, such as the USArray Transportable Array (TA) as part of the EarthScope program. Since 2004, the TA has rolled across North America, at any given time spanning a swath of approximately 800 km by 2,500 km, and thus far sampling 2% of the Earth's surface. This achievement includes all of the lower-48 U.S., southernmost Canada, and now parts of Alaska. IRIS has also facilitated specialized arrays in polar environments and on the seafloor. In all cases, the data from these arrays are freely available to the scientific community. As the community of scientists who use IRIS facilities and data look to the future they have identified a clear need for new array capabilities. In particular, as part of its Wavefields Initiative, IRIS is exploring new technologies that can enable large, dense array deployments to record unaliased wavefields at a wide range of frequencies. Large-scale arrays might utilize multiple sensor technologies to best achieve observing objectives and optimize equipment and logistical costs. Improvements in packaging and power systems can provide equipment with reduced size, weight, and power that will reduce logistical constraints for large experiments, and can make a critical difference for deployments in harsh environments or other situations where rapid deployment is required. We will review the range of existing IRIS array capabilities with an overview of previous and current deployments and examples of data and results. We will review existing IRIS projects that explore new array capabilities and highlight future directions for IRIS instrumentation facilities.

Coda Wave Analysis in Central-Western North America Using Earthscope Transportable Array Data

NASA Astrophysics Data System (ADS)

Escudero, C. R.; Doser, D. I.

2011-12-01

We determined seismic wave attenuation in the western and central United States (e.g. Washington, Oregon, California, Idaho, Nevada, Montana, Wyoming, Colorado, New Mexico, North Dakota, South Dakota, Nebraska, Kansas, Oklahoma, and Texas) using coda waves. We selected approximately twenty moderate earthquakes (magnitude between 5.5 and 6.5) located along the Mexican subduction zone, Gulf of California, southern and northern California, and off the coast of Oregon for the analysis. These events were recorded by the EarthScope transportable array (TA) network from 2008 to 2011. In this study we implemented a method based on the assumption that coda waves are single backscattered waves from randomly distributed heterogeneities to calculate the coda Q. The frequencies studied lie between 1 and 15 Hz. The scattering attenuation is calculated for frequency bands centered at 1.5, 3, 5, 7.5, 10.5, and 13.5 Hz. In this work, we present coda Q resolution maps along with a correlation analysis between coda Q and seismicity, tectonic and geology setting. We observed higher attenuation (low coda Q values) in regions of sedimentary cover, and lower attenuation (high coda Q values) in hard rock regions. Using the 4-6 Hz frequency band, we found the best general correlation between coda Q and central-western North America bedrock geology.

EarthScope's Transportable Array: Advancing Eastward

NASA Astrophysics Data System (ADS)

Busby, R. W.; Vernon, F.; Newman, R. L.; Astiz, L.

2006-12-01

EarthScope's Transportable Array has installed more than 200 high-quality broadband seismic stations over the last 3 years in the western US. These stations have a nominal spacing of 70 km and are part of an eventual 400 station array that migrates from west to east at a rate of 18 stations per month. The full 400 stations will be operating by September 2007. Stations have a residence time of about 2 years before being relocated to the next site. Throughout the continental US, 1623 sites are expected to be occupied. Standardized procedures and protocols have been developed to streamline all aspects of Transportable Array operations, from siting to site construction and installation to equipment purchasing and data archiving. Earned Value Management tools keep facility installation and operation on budget and schedule. A diverse, yet efficient, infrastructure installs and maintains the Transportable Array. Sensors, dataloggers, and other equipment are received and tested by the IRIS PASSCAL Instrument Center and shipped to regional storage facilities. To engage future geoscientists in the project, students are trained to conduct field and analytical reconnaissance to identify suitable seismic station sites. Contract personnel are used for site verification; vault construction; and installation of sensors, power, and communications systems. IRIS staff manages permitting, landowner communications, and station operations and maintenance. Seismic signal quality and metadata are quality-checked at the Array Network Facility at the University of California-San Diego and simultaneously archived at the IRIS Data Management Center in Seattle. Station equipment has been specifically designed for low power, remote, unattended operation and uses diverse two-way IP communications for real-time transmission. Digital cellular services, VSAT satellite, and commercial DSL, cable or wireless transport services are employed. Automatic monitoring of status, signal quality and earthquake event detection as well as operational alarms for low voltage and water intrusion are performed by a robust data acquisition package. This software is coupled with a host of network management tools and display managers operated by the Array Network Facility to allow managers, field personnel, and network operations staff to visualize array performance in real-time and to access historical information for diagnostics. Current data recording proficiency is 99.1%, with real-time telemetry averaging about 91%. EarthScope, IRIS and the USGS are working with regional seismic network operators, both existing and newly formed, to transition some of the Transportable Array stations into regional network assets. Each region has unique circumstances and interested parties are invited to exchange ideas on how this might be accomplished in their area. Contact busby@iris.edu for more information.

Towards a Systematic Search for Triggered Seismic Events in the USA

NASA Astrophysics Data System (ADS)

Tang, V.; Chao, K.; Van der Lee, S.

2017-12-01

Dynamic triggering of small earthquakes and tectonic tremor by small stress variations associated with passing surface waves from large-magnitude teleseismic earthquakes have been observed in seismically active regions in the western US. Local stress variations as small as 5 10 kPa can suffice to advance slip on local faults. Observations of such triggered events share certain distinct characteristics. With an eye towards an eventual application of machine learning, we began a systematic search for dynamically triggered seismic events in the USA that have these characteristics. Such a systematic survey has the potential to help us to better understand the fundamental process of dynamic triggering and hazards implied by it. Using visual inspection on top of timing and frequency based selection criteria for these seismic phenomena, our search yielded numerous false positives, indicating the challenge posed by moving from ad-hoc observations of dynamic triggering to a systematic search that also includes a catalog of non-triggering, even when sufficient stress variations are supplied. Our search includes a dozen large earthquakes that occurred during the tenure of USArray. One of these earthquakes (11 April 2012 Mw8.6 Sumatra), for example, was observed by USArray-TA stations in the Midwest and other station networks (such as PB and UW), and yielded candidate-triggered events at 413 stations. We kept 79 of these observations after closer visual inspection of the observed events suggested distinct P and S arrivals from a local earthquake, or a tremor modulation with the same period as the surface wave, among other criteria. We confirmed triggered seismic events in 63 stations along the western plate boundary where triggered events have previously been observed. We also newly found triggered tremor sources in eastern Oregon and Yellowstone, and candidate-triggered earthquake sources in New Mexico and Minnesota. Learning whether 14 of remaining candidates are confirmed as triggered events or not will provide constraints on the state of intraplate stress in the USA. Learning what it takes to discriminate between triggered events and false positives will be important for future monitoring practices.

Seismic perspectives from the western U.S. on the evolution of magma reservoirs underlying major silicic eruptions

NASA Astrophysics Data System (ADS)

Schmandt, B.; Huang, H. H.; Farrell, J.; Hansen, S. M.; Jiang, C.

2017-12-01

The western U.S. Cordillera has hosted widespread magmatic activity since the Eocene including ≥1,000 km3 silicic eruptions since 1 Ma. A review of recent seismic constraints on relatively young (≤1.1 Ma) and old (Oligocene) magmatic systems provides insight into the heterogeneity among these systems and their temporal evolution. Local seismic data vary widely but all of these systems are covered by the USArray's 70-km spacing. Among 3 young systems with ≥300 km3 silicic eruptions (Yellowstone - 0.64 Ma; Long Valley - 0.76 Ma; Valles - 1.1 Ma) only Yellowstone shows sufficiently low seismic velocities to require partial melt in the upper crust at scales visible with USArray data. Finer-scale arrays refine the shape of large (>1,000 km3) partially molten volumes in the upper and lower crust at Yellowstone, and similar studies at Long Valley and Valles indicate much smaller volumes of partial melt. Notably, Long Valley Caldera is seismically active in the upper and lower crust, has a high flux of CO2 degassing, and multi-year geodetic transients consistent with an inflating upper crustal reservoir of 2-4 km radius (compared to 20x50x5 km at Yellowstone). Upper mantle seismic imaging finds strong low velocity anomalies that require some partial melt beneath Yellowstone and Long Valley, but more ambiguous results beneath Valles. Thus, the structures of the three young large-volume silicic systems are highly variable suggesting that large reservoirs of melt in the upper crust are short-lived with respect to the ≤1.1 Ma since the last major eruption, consistent with recent inferences from geochemically constrained thermal histories of erupted crystals. Among long-extinct silicic systems, most were severely overprinted by extensional deformation. The San Juan and Mogollon Datil are exceptions with only modest deformation. These systems show low-to-average velocity crust down to a sharp Moho and relatively thin crust for their elevations. Both are consistent with a felsic to intermediate crustal column, suggesting that mafic cumulates required to produce silicic magma from basaltic inputs are not present in large quantities (>5 km layers). We infer that post-eruption foundering of mafic cumulates into the mantle occurred and was not followed by another major episode of basaltic melt input.

Using USArray Data to Explore Large-Scale Features in the Seismic Wavefield (Invited)

NASA Astrophysics Data System (ADS)

Woodward, R.; Simpson, D. W.; Busby, R. W.

2009-12-01

We explore variations in seismic waves, in both time and space, observed by the Transportable Array (TA) component of EarthScope’s USArray. The TA has collected data from over 800 station locations, stretching from the Pacific coast to the Great Plains. The stations are deployed in a 70 km grid, with each location occupied for two years, and producing continuous three-component broadband data. Given the dense station spacing and vast geographical extent of the TA network it is possible to make unprecedented direct observations of a variety of wave propagation effects. We utilize both time and frequency domain techniques to observe variations in wave propagation characteristics for individual earthquakes as well as the spatio-temporal evolution of seismic noise when observed over hours to years. Using time-domain visualizations of the propagating waves reveals clear off-great-circle propagation, wavefront distortion, and a variety of amplitude effects. Perturbations in Rayleigh wave amplitudes are pronounced, with distinct linear features in observed amplitudes across the network. At periods around 20 s these amplitude features can be spatially coherent for over 1,000 km but with sharp boundaries - marked by variations up to a factor of ten in amplitude occurring over distances as short as 70 km. We explore these observations of amplitude anomalies in greater detail to better understand their origin as source- or path-related. Our frequency domain analyses of the TA data utilize power spectra that are computed automatically, for every hour of every station-day, by the IRIS Data Management Center. The power spectra utilize hour-long data segments, with 50% overlap. The time variation of the power spectra values across the array, when rendered as individual movie frames, allow one to easily examine the evolution of both seismic noise and signals across the full spatio-temporal extent of the TA. The frequency domain view of the TA displays a number of familiar characteristics associated with seismic noise and earthquake signals. However, there are also unexpected features such as large-scale, geographically-coherent bands of high-noise which, though transient, exist for many hours. These features may be related to very weak observations of the aforementioned Rayleigh wave amplitude anomalies that are associated with elevated and sustained seismicity in particular source regions. We present examples of these observations and test hypotheses for their origin.

The Central and Eastern U.S. Seismic Network: Legacy of USArray

NASA Astrophysics Data System (ADS)

Eakins, J. A.; Astiz, L.; Benz, H.; Busby, R. W.; Hafner, K.; Reyes, J. C.; Sharer, G.; Vernon, F.; Woodward, R.

2014-12-01

As the USArray Transportable Array entered the central and eastern United States, several Federal agencies (National Science Foundation, U.S. Geological Survey, U.S. Nuclear Regulatory Commission, and Department of Energy) recognized the unique opportunity to retain TA stations beyond the original timeline. The mission of the CEUSN is to produce data that enables researchers and Federal agencies alike to better understand the basic geologic questions, background earthquake rates and distribution, seismic hazard potential, and associated societal risks of this region. The selected long-term sub-array from Transportable Array (TA) stations includes nearly 200 sites, complemented by 100 broadband stations from the existing regional seismic networks to form the Central and Eastern United States Network (CEUSN). Multiple criteria for site selection were weighed by an inter-agency TA Station Selection (TASS) Working Group: seismic noise characteristics, data availability in real time, proximity to nuclear power plants, and homogeneous distribution throughout the region. The Array Network Facility (ANF) started collecting data for CEUSN network stations since late 2013, with all stations collected since May 2014. Regional seismic data streams are collected in real-time from the IRIS Data Management Center (DMC). TA stations selected to be part of CEUSN, retain the broadband sensor to which a 100 sps channel is added, the infrasound and environmental channels, and, at some stations, accelerometers are deployed. The upgraded sites become part of the N4 network for which ANF provides metadata and can issue remote commands to the station equipment. Stations still operated by TA, but planned for CEUSN, are included in the virtual network so all stations are currently available now. By the end of 2015, the remaining TA stations will be upgraded. Data quality control procedures developed for TA stations at ANF and at the DMC are currently performed on N4 data. However, teleseismic and regional events are only picked a few times a month to fulfill data quality checks on the data. The assembled CEUSN data sets can be requested from the DMC with the _CEUSN virtual network code. Acknowledgments to Seismic Regional Network Operators: C. Ammon, J. Ebel, D. Doser, R. Hermann, A. Holland, W-Y. Kim, C. Langston, T. Owens, and M. Withers.

Mineral, Virginia earthquake illustrates seismicity of a passive-aggressive margin

NASA Astrophysics Data System (ADS)

Stein, S. A.; Pazzaglia, F. J.; Meltzer, A.; Berti, C.; Wolin, E.; Kafka, A. L.

2011-12-01

The August 2011 M5.8 Virginia earthquake illustrated again that "passive" continental margins, at which the continent and neighboring seafloor are part of the same plate, are often seismically active. This phenomenon occurs worldwide, with the east coast of North America a prime example. Examples from North to South include the 1933 M 7.3 Baffin Bay, 1929 M 7.2 Grand Banks of Newfoundland, 1755 M 6 Cape Ann, Massachusetts, and 1886 M 7 Charleston earthquakes. The mechanics of these earthquakes remains unclear. Their overall alignment along the margin suggests that they reflect reactivation of generally margin-parallel faults remaining from continental convergence and later rifting by the modern stress field. This view accords with the occurrence of the Virginia earthquake by reverse faulting on a margin-parallel NE-SW striking fault. However, it occurred on the northern edge of the central Virginia seismic zone, a seismic trend normal to the fault plane, margin, and associated structures, that has no clear geologic expression. Hence it is unclear why this and similar seismic zones have the geometry they do. Although it is tempting to correlate these zones with extensions of Atlantic fracture zones, this correlation has little explanatory power given the large number of such zones. It is similarly unclear whether these zones and the intervening seismic gaps reflect areas that are relatively more active over time, or are instead the present loci of activity that migrates. It is also possible that the presently-active zones reflect long-lived aftershocks of large prehistoric earthquakes. The forces driving the seismicity are also unclear. In general, seismic moment release decreases southward along the margin, consistent with the variation in vertical motion rates observed by GPS, suggesting that glacial-isostatic adjustment (GIA) provides some of the stresses involved. However, in the mid-Atlantic region - south of the area of significant GIA - deformed stratigraphic and geomorphic markers, localized high-relief topography, and rapid river incision show uplift of the Piedmont and Appalachians relative to the Coastal Plain for the past 10 Ma, suggesting that the seismicity reflects active and long-term deformation. These challenging questions are natural candidates for further study using new seismological and GPS data from the EarthScope program, together with geological and modeling studies. The dense deployment of seismometers in the wake of the Mineral VA earthquake and the arrival of EarthScope on the eastern seaboard in 2012 and 2013 can provide the required observations at multiple scales to better understand the mechanics of and forces driving east coast seismicity. Here we begin this study by comparing the aftershock sequence of the Mineral VA earthquake to previously recorded events in the Reading Lancaster Seismic Zone and the Central Virginia Seismic Zone.

Toward continent-scale interferometric recovery of crustal body waves through ambient seismic noise from USArray

NASA Astrophysics Data System (ADS)

Labedz, C. R.

2015-12-01

Cross-correlation of the ambient seismic noise field is now widely applied for imaging and monitoring at many scales, and has been quite successful in retrieving surface wave information useful for estimating three-dimensional shear velocity structure, anisotropy, or wave amplification and attenuation. However, the use of this approach to retrieve crustal body waves has seen less widespread use. While some studies (e.g., Zhan et al. 2010, Poli et al. 2012) have successfully recovered phases over a few hundred kilometers on continental shields, crustal body waves are not yet seen routinely over longer distances and in more structurally complex regions. In this study, we investigate the recovery of crustal body waves in the continental USA using stacked cross-correlations. The data for correlation was gathered over three to five years of continuous recording on an east-to-west line of USArray stations spanning the northern USA. Specifically, we study four parameters to determine which combination of processing produces the most robust crustal body wave estimates in this geologic setting: 1) the role of the total amount of data; 2) the impact of different processes for selecting which correlation traces are to be used or discarded from the final stacks; 3) the recoverability of waves in different directional components of the data; and 4) the geographic region of data collection. We are able to recover short period crustal S-wave phases at as far as 1500 kilometer interstation distances, which will provide unique information for future tomography models.

Upper Mantle Shear Wave Structure Beneath North America From Multi-mode Surface Wave Tomography

NASA Astrophysics Data System (ADS)

Yoshizawa, K.; Ekström, G.

2008-12-01

The upper mantle structure beneath the North American continent has been investigated from measurements of multi-mode phase speeds of Love and Rayleigh waves. To estimate fundamental-mode and higher-mode phase speeds of surface waves from a single seismogram at regional distances, we have employed a method of nonlinear waveform fitting based on a direct model-parameter search using the neighbourhood algorithm (Yoshizawa & Kennett, 2002). The method of the waveform analysis has been fully automated by employing empirical quantitative measures for evaluating the accuracy/reliability of estimated multi-mode phase dispersion curves, and thus it is helpful in processing the dramatically increasing numbers of seismic data from the latest regional networks such as USArray. As a first step toward modeling the regional anisotropic shear-wave velocity structure of the North American upper mantle with extended vertical resolution, we have applied the method to long-period three-component records of seismic stations in North America, which mostly comprise the GSN and US regional networks as well as the permanent and transportable USArray stations distributed by the IRIS DMC. Preliminary multi-mode phase-speed models show large-scale patterns of isotropic heterogeneity, such as a strong velocity contrast between the western and central/eastern United States, which are consistent with the recent global and regional models (e.g., Marone, et al. 2007; Nettles & Dziewonski, 2008). We will also discuss radial anisotropy of shear wave speed beneath North America from multi-mode dispersion measurements of Love and Rayleigh waves.

Distributions of high-velocity lower crust and seismic anisotropy across the continental U.S.: Integration of seismic, xenolith, and surface geologic data to address lithospheric dynamics and history

NASA Astrophysics Data System (ADS)

Schulte-Pelkum, V.; Mahan, K. H.; Shen, W.; Stachnik, J.; Caine, J. S.; Russo, R.

2017-12-01

Continental crust contains an integrated record of its tectonic history in its composition and preserved rock deformation fabrics. In this contribution, we highlight efforts to synthesize aspects of both of these records for the North American continent employing a variety of seismic and geologic data. We used EarthScope and pre-existing active source seismic data and selected xenolith studies to map the distribution of high-velocity lower crust, indicating mafic or garnet-bearing material, across the U.S. and assess its relationship to proposed emplacement and loss mechanisms such as under- and intraplating, collision, extension, heating, cooling, hydration, and delamination. Thin layers of high-velocity crust related to regional processes are found scattered throughout the continent. Thicker layers in large areas are found in the central and eastern U.S. in areas with thick crust, bounded roughly by the Rocky Mountain Front, which cuts across Proterozoic provinces. Hence, the difference between the two domains may reflect garnet growth with aging of continental crust in much of the central and eastern U.S., while conditions in the western U.S. appear unfavorable for growth and maintenance of thick layers of high-velocity garnet-bearing lower crust. In new research, we aim to complete a synthesis of seismic data and structural geologic data to derive constraints on the deformation history of the continent. EarthScope data have already been used to image seismic anisotropy from local scales along brittle faults and ductile shear zones to regional and continent-wide scales. These studies used multiple methods sensitive to different anisotropic parameters over a range of depths from shallow through deep crust and into the lithospheric mantle. Regional- to continent-wide comparisons of these results to geological data are currently hampered by a lack of large-scale geological data compilations. Our research seeks to facilitate ingestion of existing digital structural data (e.g., foliations, lineations, and orientations of major ductile and brittle faults) into EarthCube-funded and USGS-held databases. We will test scaling methods to link representative rock tensors via mapped rock fabric patterns to seismic wavelength-scale anisotropy in order to relate anisotropy to continental strain history.

A Community Seismic Experiment in the ENAM Primary Site

NASA Astrophysics Data System (ADS)

Van Avendonk, H. J.

2012-12-01

Eastern North America (ENAM) was chosen as a GeoPRISMS Rift Initiation and Evolution primary site because it represents a mature continental margin with onshore and offshore rift basins in which the record of extension and continental break-up is preserved. The degree to which syn-rift magmatism and preexisting lithospheric weaknesses controlled the evolution of the margin can be further investigated if we image its 3-D structure at small and large length scales with active-source and earthquake seismic imaging. In the Summer of 2012 we submitted a proposal to the US National Science Foundation for an ambitious plan for data acquisition on a 400 km wide section of the mid-Atlantic East Coast margin around Cape Hatteras, from unextended continental lithosphere onshore to mature oceanic lithosphere offshore. This area includes an important along-strike transition in the morphology of the margin from the Carolina Trough to the Baltimore Canyon Trough, and two major fracture zones that are associated with significant offsets at the modern Mid-Atlantic Ridge. The study area also covers several features representing the post-rift modification of the margin by slope instability and fluid flow. As the Earthscope Transportable Array reaches the East Coast of the US in 2013 and 2014, we will have an unprecedented opportunity to image the detailed structure of the rifted margin. To make effective use of the research infrastructure, including the seismic vessel R/V Marcus Langseth, the Earthscope seismic instrumentation, and US OBS Instrument Pool, we propose to collect a suite of seismic data at the mid-Atlantic margin in the context of a community-driven experiment with completely open data access. This multi-faceted seismic experiment offers an immense opportunity for education of young scientists. We propose an integrated education effort during and after acquisition. The science and field parties for data acquisition will largely consist of young scientists, who will be chosen by application. Following the cruise, we propose to hold two short courses on multi-channel seismic reflection and wide-angle reflection and refraction data processing using the new seismic data. The acquisition of all seismic data, archiving of the data in existing data bases, and distribution to the community will take two years. Afterwards, proposals developed by any member of the science community can be submitted for further data analysis and testing of current scientific hypotheses regarding the evolution and dynamics of the ENAM margin.

Lithosphere-asthenosphere interaction beneath the western United States from the joint inversion of body-wave traveltimes and surface-wave phase velocities

USGS Publications Warehouse

Obrebski, M.; Allen, R.M.; Pollitz, F.; Hung, S.-H.

2011-01-01

The relation between the complex geological history of the western margin of the North American plate and the processes in the mantle is still not fully documented and understood. Several pre-USArray local seismic studies showed how the characteristics of key geological features such as the Colorado Plateau and the Yellowstone Snake River Plains are linked to their deep mantle structure. Recent body-wave models based on the deployment of the high density, large aperture USArray have provided far more details on the mantle structure while surface-wave tomography (ballistic waves and noise correlations) informs us on the shallow structure. Here we combine constraints from these two data sets to image and study the link between the geology of the western United States, the shallow structure of the Earth and the convective processes in mantle. Our multiphase DNA10-S model provides new constraints on the extent of the Archean lithosphere imaged as a large, deeply rooted fast body that encompasses the stable Great Plains and a large portion of the Northern and Central Rocky Mountains. Widespread slow anomalies are found in the lower crust and upper mantle, suggesting that low-density rocks isostatically sustain part of the high topography of the western United States. The Yellowstone anomaly is imaged as a large slow body rising from the lower mantle, intruding the overlying lithosphere and controlling locally the seismicity and the topography. The large E-W extent of the USArray used in this study allows imaging the 'slab graveyard', a sequence of Farallon fragments aligned with the currently subducting Juan de Fuca Slab, north of the Mendocino Triple Junction. The lithospheric root of the Colorado Plateau has apparently been weakened and partly removed through dripping. The distribution of the slower regions around the Colorado Plateau and other rigid blocks follows closely the trend of Cenozoic volcanic fields and ancient lithospheric sutures, suggesting that the later exert a control on the locus of magmato-tectonic activity today. The DNA velocity models are available for download and slicing at http://dna.berkeley.edu. ?? 2011 The Authors Geophysical Journal International ?? 2011 RAS.

Widespread Triggering of Earthquakes in the Central US by the 2011 M9.0 Tohoku-Oki Earthquake

NASA Astrophysics Data System (ADS)

Rubinstein, J. L.; Savage, H. M.

2011-12-01

The strong shaking of the 2011 M9.0 off-Tohoku earthquake triggered tectonic tremor and earthquakes in many locations around the world. We analyze broadband records from the USARRAY to identify triggered seismicity in more than 10 different locations in the Central United States. We identify triggered events in many states including: Kansas, Nebraska, Arkansas, Minnesota, and Iowa. The locally triggered earthquakes are obscured in broadband records by the Tohoku-Oki mainshock but can be revealed with high-pass filtering. With the exception of one location (central Arkansas), the triggered seismicity occurred in regions that are seismically quiet. The coincidence of this seismicity with the Tohoku-Oki event suggests that these earthquakes were triggered. The triggered seismicity in Arkansas occurred in a region where there has been an active swarm of seismicity since August 2010. There are two lines of evidence to indicate that the seismicity in Arkansas is triggered instead of part of the swarm: (1) we observe two earthquakes that initiate coincident with the arrival of shear wave and Love wave; (2) the seismicity rate increased dramatically following the Tohoku-Oki mainshock. Our observations of widespread earthquake triggering in regions thought to be seismically quiet remind us that earthquakes can occur in most any location. Studying additional teleseismic events has the potential to reveal regions with a propensity for earthquake triggering.

Engaging teachers, interpreters and emergency management educators in disaster preparedness and EarthScope science through joint professional development workshops (Invited)

NASA Astrophysics Data System (ADS)

Pratt-Sitaula, B. A.; Lillie, R. J.; Butler, R. F.; Hunter, N.; Magura, B.; Groom, R.; Hedeen, C. D.; Johnson, J. A.; Ault, C.; Olds, S. E.

2013-12-01

The same geological forces that form the spectacular beaches and headlands of the Pacific Northwest also threaten lives and infrastructure with earthquakes and tsunamis. A new project called the Cascadia EarthScope, Earthquake, and Tsunami Education Program (CEETEP), is helping to mitigate the effects of these potential disasters through collaboration building and professional development for K-12 teachers, park and museum interpreters, and emergency management outreach educators in communities along the Oregon and Washington coast. Tens of thousands of Oregon and Washington residents live within severe earthquake-shaking and tsunami-inundation zones, and millions of tourists visit state and federal parks in these same areas each year. Teachers in the K-12 school systems convey some basics about geological hazards to their students, and park rangers and museum educators likewise engage visitors at their sites. Emergency management educators make regular presentations to local residents about disaster preparedness. CEETEP is strengthening these efforts by providing community-based workshops that bring together all of these professionals to review the basic science of earthquakes and tsunamis, learn about EarthScope and other research efforts that monitor the dynamic Earth in the region, and develop ways to collectively engage students and the general public on the mitigation of coastal geologic hazards. As part of a nationwide effort, the NSF EarthScope Program has been deploying hundreds of seismic, GPS, and other geophysical instruments to measure movement of the Earth's crust and detect earthquakes along the Cascadia Subduction Zone. These instruments provide detail for ongoing research showing that coastal regions are storing energy that will be released in the next great Cascadia earthquake, with the resulting tsunami arriving onshore in 30 minutes or less. CEETEP is helping to convey these cutting-edge findings to coastal educators and fulfill EarthScope's intended broader impact of contributing 'to the mitigation of risks from geological hazards ... and the public's understanding of the dynamic Earth.' Preliminary results from CEETEP's 2013 August and October workshops will be presented.

An EarthScope Plate Boundary Observatory Progress Report

NASA Astrophysics Data System (ADS)

Jackson, M.; Anderson, G.; Blume, F.; Walls, C.; Coyle, B.; Feaux, K.; Friesen, B.; Phillips, D.; Hafner, K.; Johnson, W.; Mencin, D.; Pauk, B.; Dittmann, T.

2007-12-01

UNAVCO is building and operating the Plate Boundary Observatory (PBO), part of the NSF-funded EarthScope project to understand the structure, dynamics, and evolution of the North American continent. When complete in October 2008, the 875 GPS, 103 strain and seismic, and 28 tiltmeters stations will comprise the largest integrated geodetic and seismic network in United States and the second largest in the world. Data from the PBO network will facilitate research into plate boundary deformation with unprecedented scope and detail. As of 1 September 2007, UNAVCO had completed 680 PBO GPS stations and had upgraded 89% of the planned PBO Nucleus stations. Highlights of the past year's work include the expansion of the Alaska subnetwork to 95 continuously-operating stations, including coverage of Akutan and Augustine volcanoes and reconnaissance for future installations on Unimak Island; the installation of nine new stations on Mt. St. Helens; and the arrival of 33 permits for station installations on BLM land in Nevada. The Augustine network provided critical data on magmatic and volcanic processes associated with the 2005-2006 volcanic crisis, and has expanded to a total of 11 stations. Please visit http://pboweb.unavco.org/?pageid=3 for further information on PBO GPS network construction activities. As of September 2007, 41 PBO borehole stations had been installed and three laser strainmeter stations were operating, with a total of 60 borehole stations and 4 laser strainmeters expected by October 2007. In response to direction from the EarthScope community, UNAVCO installed a dense network of six stations along the San Jacinto Fault near Anza, California; installed three of four planned borehole strainmeter stations on Mt. St. Helens; and has densified coverage of the Parkfield area. Please visit http://pboweb.unavco.org/?pageid=8 for more information on PBO strainmeter network construction progress. The combined PBO/Nucleus GPS network provides 350 GB of raw standard rate data, with special downloads of more than 250 GB of high-rate GPS data following large earthquakes in Russia, Tonga, and Peru, as well as for community requests. The standard rate GPS data are processed routinely to generate data products including station position time series, velocity vectors, and related information, and all data products are available from the UNAVCO Facility archive. The PBO seismic network seismic network has provided 201 GB of raw data, which are available via Antelope and Earthworm from PBO and via the IRIS Data Management Center (DMC); we provide data to seismic networks operated from Caltech, UCSD, UCSB, University of Washington, and the Pacific Geosciences Center in Sidney, BC. The PBO strainmeter network has provided 93 GB of raw data, available in both raw native format and SEED format from the Northern California Earthquake Data Center and the IRIS DMC, along with higher-level products such as cleaned strain time series and related information. Please visit http://pboweb.unavco.org/gps_data and http://pboweb.unavco.org/strain_data for more information on PBO GPS and strainmeter/seismic data products, respectively.

Broadband Array Analysis of the 2005 Episodic Tremor and Slip Event in Northern Cascadia

NASA Astrophysics Data System (ADS)

Wech, A.; Creager, K.; McCausland, W.; Frassetto, A.; Qamar, A.; Derosier, S.; Carmichael, J.; Malone, S.; Johnson, D.

2005-12-01

The region of Cascadia from the Olympic Mountains through southern Vancouver Island and down-dip of the subduction megathrust has repeatedly experienced episodes of slow slip. This episodic slip, which has been observed to take place over a period of two to several weeks, is accompanied by a seismic tremor signal. Based on the average recurrence interval of 14 months, the next episodic tremor and slip (ETS) event should occur within six weeks of mid-September, 2005. Indeed, it appears to have begun on September 3, as this abstract was being written. In order to record this anticipated event, we deployed an array of 11 three-component seismometers on the northern side of the Olympic Peninsula augmenting Pacific Northwest Seismographic Network stations as well as the first few EarthScope BigFoot stations and Plate Boundary Observatory borehole seismometers. This seismic array was comprised of six short-period and five broadband instruments with spacings of 500 m and 2200 m respectively. In conjunction with this Earthscope seismic deployment, we also installed a dense network of 29 temporary, continuous GPS stations across the entire Olympic Peninsula to integrate seismic and geodetic observations. One of the primary goals of this research is to utilize the broadband instrumentation in the array to investigate the possible correlation of low frequency energy with the rest of the tremor activity. ETS has been carefully investigated at high-frequency (seismic tremor at 2-6 Hz) and very low-frequency (slip occurring over weeks, observed by GPS). An important goal of this experiment is to investigate the possibility that the tremor generates intermediate, low-frequency signals. Preliminary analysis of short-period array recordings of the July, 2004 ETS event suggests that the tremor displays signs of lower-frequency energy (~0.5 Hz) correlated with its higher frequency activity. Our array should enable us to distinguish low- frequency signals originating in the direction of high-frequency tremor from noise in other directions. We will present an analysis of the low-frequency energy associated with this slip event.

CAFE: a seismic investigation of water percolation in the Cascadia subduction zone

NASA Astrophysics Data System (ADS)

Rondenay, S.; Abers, G. A.; Creager, K. C.; Malone, S. D.; MacKenzie, L.; Zhang, Z.; van Keken, P. E.; Wech, A. G.; Sweet, J. R.; Melbourne, T. I.; Hacker, B. R.

2008-12-01

Subduction zones transport water into the Earth's interior. The subsequent release of this water through dehydration reactions may trigger intraslab earthquakes and arc volcanism, regulate slip on the plate interface, control plate buoyancy, and regulate the long-term budget of water on the planet's surface. As part of Earthscope, we have undertaken an experiment named CAFE (Cascadia Arrays for Earthscope) seeking to better constrain these effects in the Cascadia subduction zone. The basic experiment has four components: (1) a 47-element broadband imaging array of Flexible Array instruments integrated with Bigfoot; (2) three small-aperture seismic arrays with 15 additional short-period instruments near known sources of Episodic Tremor and Slip (ETS) events; (3) analysis of the PBO and PANGA GPS data sets to define the details of episodic slip events; and (4) integrative modeling with complementary constraints from petrology and geodynamics. Here, we present a summary of the results that have been obtained to date by CAFE, with a focus on high-resolution seismic imaging. A 250 km-long by 120 km-deep seismic profile extending eastward from the Washington coast was generated by 2-D Generalized Radon Transform Inversion of the broadband data. It images the subducted crust as a shallow-dipping, low-velocity layer from 20km depth beneath the coast to 40km depth beneath the forearc. The termination of the low-velocity layer is consistent with the depth at which hydrated metabasalts of the subducted crust are expected to undergo eclogitization, a reaction that is accompanied by the release of water and an increase in seismic velocities. Slab earthquakes are located in both the oceanic crust and mantle at depths <40 km, and exclusively in the oceanic mantle at greater depth, as would be expected if they are related to slab dehydration. Two ETS events have occurred during the course of the deployment. They were precisely located and are confined to the region above which the crust exhibits low-velocities and is believed to undergo progressive dehydration, further supporting the proposition that water plays a role in ETS.

One billion year-old Mid-continent Rift leaves virtually no clues in the mantle

NASA Astrophysics Data System (ADS)

Bollmann, T. A.; Frederiksen, A. W.; van der Lee, S.; Wolin, E.; Revenaugh, J.; Wiens, D.; Darbyshire, F. A.; Aleqabi, G. I.; Wysession, M. E.; Stein, S.; Jurdy, D. M.

2017-12-01

We measured the relative arrival times of more than forty-six thousand teleseismic P waves recorded by seismic stations of Earthscope's Superior Province Rifting Earthscope Experiment (SPREE) and combined them with a similar amount of such measurements from other seismic stations in the larger region. SPREE recorded seismic waves for two and a half years around the prominent, one billion year-old Mid-continent Rift structure. The curvilinear Mid-continent Rift (MR) is distinguished by voluminous one billion year-old lava flows, which produce a prominent gravity high along the MR. As for other seismic waves, these lava flows along with their underplated counterpart, slightly slow down the measured teleseismic P waves, on average, compared to P waves that did not traverse structures beneath the Mid-continent Rift. However, the variance in the P wave arrival times in these two groups is nearly ten times higher than their average difference. In a seismic-tomographic inversion, we mapped all measured arrival times into structures deep beneath the crust, in the Earth's mantle. Beneath the crust we generally find relatively high P velocities, indicating relatively cool and undeformable mantle structures. However, the uppermost mantle beneath the MR shows several patches of slightly decreased P velocities. These patches are coincident with where the gravity anomalies peak, in Iowa and along the northern Minnesota/Wisconsin border. We will report on the likelihood that these anomalies are indeed a remaining mantle-lithospheric signature of the MR or whether these patches indirectly reflect the presence of the lava flows and their underplated counterparts at the crust-mantle interface. Other structures of interest and of varying depth extent in our tomographic image locate at 1) the intersection of the Superior Craton with the Penokean Province and the Marshfield Terrane west of the MR in southern Minnesota, 2) the intersection of the Penokean, Yavapai, and Mazatzal Terranes along the eastern edge of the Michigan arm of the MR, and 3) beneath Lake Nipigon, north of Lake Superior. Our tomographic image also reveals an intricate distribution of deep high-velocity anomalies, including in the lower mantle, potentially related to Mesozoic subduction of the Kula and/or Farallon Plates.

Crustal Seismic Velocity Models of Texas

NASA Astrophysics Data System (ADS)

Borgfeldt, T.; Walter, J. I.; Frohlich, C.

2016-12-01

Crustal seismic velocity models are used to locate earthquake hypocenters. Typically, one dimensional velocity models are 3 - 8 fixed-thickness layers of varying P and S velocities with depth. On occasion, the layers of the upper crust (0-2 kilometers) are constrained with well log data from nearby wells, when available. Past velocity models used in Texas to locate earthquakes were made with little regard to deeper geologic units because shallow earthquakes with a localized seismic network only require velocity models of the upper crust. A recently funded statewide seismic network, TexNet, will require deeper crustal velocity models. Using data of geologic provinces, tectonics, sonic logs, tomography and receiver function studies, new regional velocity models of the state of Texas will allow researchers to more accurately locate hypocenters of earthquakes. We tested the accuracy of the initial models and then refine the layers of the 1-D regional models by using previously located earthquakes the USArray Transportable Array with earthquake location software. Geologic information will be integrated into a 3D velocity model at 0.5 degreee resolution for the entire state of Texas.

Delivering the EarthScope Transportable Array as a Community Asset

NASA Astrophysics Data System (ADS)

Busby, R. W.; Woodward, R.; Simpson, D. W.; Hafner, K.

2009-12-01

The Transportable Array element of EarthScope/USArray is a culmination of years of coordination and planning for a large science initiative via the NSF MREFC program. US researchers and the IRIS Consortium conceived of the science objectives for a continental scale array and, together with the geodetic (PBO) and fault drilling (SAFOD) communities and NSF, successfully merged these scientific objectives with a compelling scientific and technical proposal, accompanied with the budget and schedule to accomplish it. The Transportable Array is now an efficient and exacting execution of an immense technical challenge that, by many measures, is yielding exciting science return, both expected and unanticipated. The technical facility is first-rate in its implementation, yet responsive to science objectives and discovery, actively engaging the community in discussion and new direction. The project is carried out by a core of dedicated and professional staff , guided and advised through considerable feedback from science users who have unprecedented access to high-quality data. This, in a sense, lets seismologists focus on research, rather than be administrators, drivers, shippers, battery mules, electronic technicians and radio hams. Now that USArray is operational, it is interesting to reflect on whether the TA, as a professionally executed project, could succeed as well if it were an independent endeavor, managed and operated outside of the resources developed and available through IRIS and its core programs. We detail how the support the USArray facility provides improves data accessibility and enhances interdisciplinary science. We suggest that the resources and community leadership provided by the IRIS Consortium, and the commitment to the principle of free and open data access, have been basic underpinnings for the success of the TA. This involvement of community-based, scientific leadership in the development of large facilities should be considered in planning future large Earth science or even basic science endeavors. The Global Seismographic Network provides another example where, with strong scientific leadership, the technical objectives have returned far more than expected results from all manner of application of new techniques to high quality data. Again, the key ingredient may be that the project oversight is driven by scientists with free and open access to data and broad and evolving expectations as to how the facility might be applied towards research objectives. Major projects must clearly follow defined plans and budgets; but, while it is important to have managers to motivate schedules and control costs, the energy, vigor and effort to optimize new measures and discover new applications derive from the insights and enthusiasm of the science community.

Seismicity in Pennsylvania: Evidence for Anthropogenic Events?

NASA Astrophysics Data System (ADS)

Homman, K.; Nyblade, A.

2015-12-01

The deployment and operation of the USArray Transportable Array (TA) and the PASEIS (XY) seismic networks in Pennsylvania during 2013 and 2014 provide a unique opportunity for investigating the seismicity of Pennsylvania. These networks, along with several permanent stations in Pennsylvania, resulted in a total of 104 seismometers in and around Pennsylvania that have been used in this study. Event locations were first obtained with Antelope Environmental Monitoring Software using P-wave arrival times. Arrival times were hand picked using a 1-5 Hz bandpass filter to within 0.1 seconds. Events were then relocated using a velocity model developed for Pennsylvania and the HYPOELLIPSE location code. In this study, 1593 seismic events occurred between February 2013 and December 2014 in Pennsylvania. These events ranged between magnitude (ML) 1.04 and 2.89 with an average MLof 1.90. Locations of the events occur across the state in many areas where no seismicity has been previously reported. Preliminary results indicate that most of these events are related to mining activity. Additional work using cross-correlation techniques is underway to examine a number of event clusters for evidence of hydraulic fracturing or wastewater injection sources.

Background Lamb waves in the Earth's atmosphere

NASA Astrophysics Data System (ADS)

Nishida, K.; Kobayashi, N.; Fukao, Y.

2013-12-01

Lamb waves of the Earth's atmosphere in the millihertz band have been considered as transient phenomena excited only by large events [e.g. the major volcanic eruption of Krakatoa in 1833, the impact of Siberian meteorite in 1908, the testing of large nuclear tests and the huge earthquakes, Garrett1969]. In a case of the solid Earth, observation of background free oscillations in the millihertz band-now known as Earth's background free oscillations or seismic hum, has been firmly established. Above 5 mHz, their dominant excitation sources are oceanic infragravity waves. At 3.7 and 4.4 mHz an elasto-acoustic resonance between the solid Earth and the atmosphere was observed [Nishida et al., 2000]. These seismic observations show that the contribution of atmospheric disturbances to the seismic hum is dominant below 5 mHz. Such contribution implies background excitations of acoustic-gravity waves in this frequency range. For direct detection of the background acoustic-gravity waves, our group conducted observations using an array of barometers [Nishida et al. 2005]. However, the spatial scale of the array of about 10 km was too small to detect acoustic modes below 10 mHz. Since then, no direct observations of these waves have been reported. In 2011, 337 high-resolution microbarometers were installed on a continental scale at USArray Transportable Array. The large and dense array enables us to detect the background atmospheric waves. Here, we show the first evidence of background Lamb waves in the Earth's atmosphere from 0.2 to 10 mHz, based on the array analysis of microbarometer data from the USArray in 2012. The observations suggest that the excitation sources are atmospheric disturbances in the troposphere. Theoretically, their energy in the troposphere tunnels into the thermosphere at a resonant frequency via thermospheric gravity wave, where the observed amplitudes indeed take a local minimum. The energy leak through the frequency window could partly contribute to thermospheric wave activity. Tropospheric disturbances exciting background Lamb waves may also be responsible for seismic hum at frequencies below 5 mHz.

Geophysical character of the intraplate Wabash Fault System from the Wabash EarthScope FlexArray

NASA Astrophysics Data System (ADS)

Conder, J. A.; Zhu, L.; Wood, J. D.

2017-12-01

The Wabash Seismic Array was an EarthScope funded FlexArray deployment across the Wabash Fault System. The Wabash system is long known for oil and gas production. The fault system is often characterized as an intraplate seismic zone as it has produced several earthquakes above M4 in the last 50 years and potentially several above M7 in the Holocene. While earthquakes are far less numerous in the Wabash system than in the nearby New Madrid seismic zone, the seismic moment is nearly twice that of New Madrid over the past 50 years. The array consisted of 45 broadband instruments deployed across the axis to study the larger structure and 3 smaller phased arrays of 9 short-period instruments each to get a better sense of the local seismic output of smaller events. First results from the northern phased array indicate that seismicity in the Wabash behaves markedly differently than in New Madrid, with a low b-value around 0.7. Receiver functions show a 50 km thick crust beneath the system, thickening somewhat to the west. A variable-depth, positive-amplitude conversion in the deep crust gives evidence for a rift pillow at the base of the system within a dense lowermost crustal layer. Low Vs and a moderate negative amplitude conversion in the mid crust suggest a possible weak zone that could localize deformation. Shear wave splitting shows fast directions consistent with absolute plate motion across the system. Split times drop in magnitude to 0.5-0.7 seconds within the valley while in the 1-1.5 second range outside the valley. This magnitude decrease suggests a change in mantle signature beneath the fault system, possibly resulting from a small degree of local flow in the asthenosphere either along axis (as may occur with a thinned lithosphere) or by vertical flow (e.g., from delamination or dripping). We are building a 2D tomographic model across the region, relying primarily on teleseismic body waves. The tomography will undoubtedly show variations in crustal structure that will give additional context to the receiver function results. Possibly more importantly, the lithospheric structure will discriminate between hypotheses of mantle flow required to give the observed shear wave splitting signature.

High-resolution probing of inner core structure with seismic interferometry

NASA Astrophysics Data System (ADS)

Huang, Hsin-Hua; Lin, Fan-Chi; Tsai, Victor C.; Koper, Keith D.

2015-12-01

Increasing complexity of Earth's inner core has been revealed in recent decades as the global distribution of seismic stations has improved. The uneven distribution of earthquakes, however, still causes a biased geographical sampling of the inner core. Recent developments in seismic interferometry, which allow for the retrieval of core-sensitive body waves propagating between two receivers, can significantly improve ray path coverage of the inner core. In this study, we apply such earthquake coda interferometry to 1846 USArray stations deployed across the U.S. from 2004 through 2013. Clear inner core phases PKIKP2 and PKIIKP2 are observed across the entire array. Spatial analysis of the differential travel time residuals between the two phases reveals significant short-wavelength variation and implies the existence of strong structural variability in the deep Earth. A linear N-S trending anomaly across the middle of the U.S. may reflect an asymmetric quasi-hemispherical structure deep within the inner core with boundaries of 99°W and 88°E.

Detecting Seismic Activity with a Covariance Matrix Analysis of Data Recorded on Seismic Arrays

NASA Astrophysics Data System (ADS)

Seydoux, L.; Shapiro, N.; de Rosny, J.; Brenguier, F.

2014-12-01

Modern seismic networks are recording the ground motion continuously all around the word, with very broadband and high-sensitivity sensors. The aim of our study is to apply statistical array-based approaches to processing of these records. We use the methods mainly brought from the random matrix theory in order to give a statistical description of seismic wavefields recorded at the Earth's surface. We estimate the array covariance matrix and explore the distribution of its eigenvalues that contains information about the coherency of the sources that generated the studied wavefields. With this approach, we can make distinctions between the signals generated by isolated deterministic sources and the "random" ambient noise. We design an algorithm that uses the distribution of the array covariance matrix eigenvalues to detect signals corresponding to coherent seismic events. We investigate the detection capacity of our methods at different scales and in different frequency ranges by applying it to the records of two networks: (1) the seismic monitoring network operating on the Piton de la Fournaise volcano at La Réunion island composed of 21 receivers and with an aperture of ~15 km, and (2) the transportable component of the USArray composed of ~400 receivers with ~70 km inter-station spacing.

Evaluating the Reverse Time Migration Method on the dense Lapnet / Polenet seismic array in Europe

NASA Astrophysics Data System (ADS)

Dupont, Aurélien; Le Pichon, Alexis

2013-04-01

In this study, results are obtained using the reverse time migration method used as benchmark to evaluate the implemented method by Walker et al., (2010, 2011). Explosion signals recorded by the USArray and extracted from the TAIRED catalogue (TA Infrasound Reference Event Database user community / Vernon et al., 2012) are investigated. The first one is an explosion at Camp Minden, Louisiana (2012-10-16 04:25:00 UTC) and the second one is a natural gas explosion near Price, Utah (2012-11-20 15:20:00 UTC). We compare our results to automatic solutions (www.iris.edu/spud/infrasoundevent). The good agreement between both solutions validates our detection method. In a second time, we analyse data from the Lapnet / Polenet dense seismic network (Kozlovskaya et al., 2008). Detection and location in two-dimensional space and time of infrasound events presumably due to acoustic-to-seismic coupling, during the 2007-2009 period in Europe, are presented. The aim of this work is to integrate near-real time network performance predictions at regional scales to improve automatic detection of infrasonic sources. The use of dense seismic networks provides a valuable tool to monitor infrasonic phenomena, since seismic location has recently proved to be more accurate than infrasound locations due to the large number of seismic sensors.

Seismic Observations of the Mid-Pacific Large Low Shear Velocity Province

NASA Astrophysics Data System (ADS)

Chan, A.; Helmberger, D. V.; Sun, D.; Li, D.; Jackson, J. M.

2015-12-01

Seismic data from earthquakes originating in the Fiji-Tonga region exhibits waveform complexity of a number of phases which may be attributed to various structures along ray paths to stations of USArray, including anomalous structures at the core-mantle boundary. The data shows variation in multipathing, that is, the presence of secondary arrivals following the S phase at diffracted distances (Sdiff) which suggests that the waveform complexity is due to structures at the eastern edge of the mid-Pacific Large Low Shear Velocity Province (LLSVP). This study examines data from earthquake events while the Transportable Array portion of USArray was situated in the midwest United States, reinforcing previous studies that indicate late arrivals occurring as long as 26 seconds after the primary arrivals (To et al., 2011). Using earth flattening transformations and finite difference methods, simulations of tapered wedge structures of low velocity material allow for wave energy trapping, producing the observed waveform complexity and delayed arrivals at large distances, with such structures having characteristic properties of, for example, a height of 70 km, in-plane extent more than 1000 km, and shear wave velocity drop of 3% at the top to 15% at the bottom relative to PREM. Differential arrival times for SH and SV components suggest anisotropy and possible wave propagation through downgoing slabs beneath the source region. The arrivals of the SPdKS phase further support the presence of an ultra-low velocity zone (ULVZ) within a two-humped LLSVP. Some systematic delays in arrival times of multiple phases for distances less than 102º are accounted for and attributed to the presence of a mantle slab underneath the continental United States. Comparisons to seismic data from earthquakes originating from other locations further constrain depths of the deep mantle structures. Possible explanations include iron-enrichment of deep mantle phases.

The 2008 Mw 6.0 Wells, Nevada Earthquake Sequence

NASA Astrophysics Data System (ADS)

Smith, K.; Depolo, D.; Torrisi, J.; Edwards, N.; Biasi, G.; Slater, D.

2008-12-01

The Mw 6.0 February 21, 2008 (06:16 AM PDT) Wells, Nevada normal faulting earthquake occurred in Town Creek Flat about 8 km northeast of the small community of Wells. A preliminary set of about 1000 aftershock relocations clearly defines a 55-60 degree southeast dipping fault plane. The structure projects to the surface along the southern end of the Snake Range, although no surface offsets have been identified. The earthquake occurred east of the Ruby Mountains and Snake Range west dipping range front faults, possibly on a northern extension of an east dipping normal fault system on the eastern side of the East Humbolt Range. The depth of the mainshock is estimated to be 10.5 km with the aftershock sequence extending to about 15 km. Typical of moderate sized Basin and Range earthquakes, the early aftershock period included several earthquakes of M > 4 and these were felt strongly by the residents of Wells. From the preliminary relocations, the source radius of the mainshock is estimated to be about 4 km, resulting in an estimated displacement of 55 to 83 cm and static stress drop of 72 to 86 bars, depending on the seismic moment estimate used. Aftershock relocations suggest a radial rupture mechanism. Fortunately, the EarthScope USArray network was operating in Nevada at the time of the event and provided unique controls on the mainshock and early aftershock locations. The earthquake occurred in an area of relatively low seismic hazard and the only permanent seismograph in the region was the U.S. National Network broadband station east of the Ruby Mountains south of Wells. The University of Utah and University of Nevada deployed locally recorded strong motion instruments in the Wells area. Also, an 8 station IP telemetered strong motion network, jointly deployed by the U.S. Geological Survey and University of Nevada Reno, provided real-time data for quick high-quality aftershock relocations and ground motion estimates. In addition, the University of Utah established several telemetered analog stations for improved aftershock locations. IP data communications was routed through the Nevada Department of Information Technology microwave communications site north of Wells. The aftershock deployment was not possible without the considerable support of a number of public and private agencies in the Wells area and the Wells community itself. Many unreinforced masonry structures in old-town Wells, dating to the early 1900's, experienced significant damage. There was also damage to homes and businesses within the community, including the local High School, but fortunately there were no serious injuries associated with the earthquake.

Mantle Circulation Models with variational data assimilation: Inferring past mantle flow and structure from plate motion histories and seismic tomography

NASA Astrophysics Data System (ADS)

Bunge, H.; Hagelberg, C.; Travis, B.

2002-12-01

EarthScope will deliver data on structure and dynamics of continental North America and the underlying mantle on an unprecedented scale. Indeed, the scope of EarthScope makes its mission comparable to the large remote sensing efforts that are transforming the oceanographic and atmospheric sciences today. Arguably the main impact of new solid Earth observing systems is to transform our use of geodynamic models increasingly from conditions that are data poor to an environment that is data rich. Oceanographers and meteorologists already have made substantial progress in adapting to this environment, by developing new approaches of interpreting oceanographic and atmospheric data objectively through data assimilation methods in their models. However, a similarly rigorous theoretical framework for merging EarthScope derived solid Earth data with geodynamic models has yet to be devised. Here we explore the feasibility of data assimilation in mantle convection studies in an attempt to fit global geodynamic model calculations explicitly to tomographic and tectonic constraints. This is an inverse problem not quite unlike the inverse problem of finding optimal seismic velocity structures faced by seismologists. We derive the generalized inverse of mantle convection from a variational approach and present the adjoint equations of mantle flow. The substantial computational burden associated with solutions to the generalized inverse problem of mantle convection is made feasible using a highly efficient finite element approach based on the 3-D spherical fully parallelized mantle dynamics code TERRA, implemented on a cost-effective topical PC-cluster (geowulf) dedicated specifically to large-scale geophysical simulations. This dedicated geophysical modeling computer allows us to investigate global inverse convection problems having a spatial discretization of less than 50 km throughout the mantle. We present a synthetic high-resolution modeling experiment to demonstrate that mid-Cretaceous mantle structure can be inferred accurately from our inverse approach assuming present-day mantle structure is well-known, even if an initial first guess assumption about the mid-Cretaceous mantle involved only a simple 1-D radial temperature profile. We suggest that geodynamic inverse modeling should make it possible to infer a number of flow parameters from observational constraints of the mantle.

Seismic structure of the central US crust and upper mantle: Uniqueness of the Reelfoot Rift

USGS Publications Warehouse

Pollitz, Fred; Mooney, Walter D.

2014-01-01

Using seismic surface waves recorded with Earthscope's Transportable Array, we apply surface wave imaging to determine 3D seismic velocity in the crust and uppermost mantle. Our images span several Proterozoic and early Cambrian rift zones (Mid-Continent Rift, Rough Creek Graben—Rome trough, Birmingham trough, Southern Oklahoma Aulacogen, and Reelfoot Rift). While ancient rifts are generally associated with low crustal velocity because of the presence of thick sedimentary sequences, the Reelfoot Rift is unique in its association with low mantle seismic velocity. Its mantle low-velocity zone (LVZ) is exceptionally pronounced and extends down to at least 200 km depth. This LVZ is of variable width, being relatively narrow (∼50km">∼50km wide) within the northern Reelfoot Rift, which hosts the New Madrid Seismic Zone (NMSZ). We hypothesize that this mantle volume is weaker than its surroundings and that the Reelfoot Rift consequently has relatively low elastic plate thickness, which would tend to concentrate tectonic stress within this zone. No other intraplate ancient rift zone is known to be associated with such a deep mantle low-velocity anomaly, which suggests that the NMSZ is more susceptible to external stress perturbations than other ancient rift zones.

EarthScope National Office Education and Outreach Program: 2013 Update on Activities and Outcomes

NASA Astrophysics Data System (ADS)

Semken, S. C.; Robinson, S.; Bohon, W.; Schwab, P.; Arrowsmith, R.; Garnero, E. J.; Fouch, M. J.; Pettis, L.; Baumback, D.; Dick, C.

2013-12-01

The EarthScope Program (www.earthscope.org) funded by the National Science Foundation, fosters interdisciplinary exploration of the geologic structure and evolution of the North American continent by means of seismology, geodesy, magnetotellurics, in-situ fault-zone sampling, geochronology, and high-resolution topographic measurements. Data and findings from EarthScope continue to transform geoscientific studies throughout the Earth, enhance understanding and mitigation of hazards, and inform applications of geoscience toward environmental sustainability. The EarthScope Program also marshals significant resources and opportunities for education and outreach (E&O) in the Earth system sciences. The EarthScope National Office (ESNO) at Arizona State University serves all EarthScope stakeholders, including the EarthScope Steering Committee, researchers, educators, students, and the general public. ESNO supports and promotes E&O through social media and web-hosted resources, newsletters and published articles, E&O workshops for informal educators (interpreters), assistance to grassroots K-12 STEM teacher professional development projects (typically led by EarthScope researchers), continuing education for researchers, collaborations with other Earth-science E&O providers, and biannual national conferences. The EarthScope E&O program at ESNO leads and supports wide dissemination of the data, findings, and legacy of EarthScope. Notable activities in 2013 include expansion of social-media and web-based content, two Interpretive Workshops in the eastern United States, the Great ShakeOut, the EarthScope National Meeting in Raleigh, and continuing partnerships with affiliated E&O providers. The EarthScope National Office is supported by the National Science Foundation under grants EAR-1101100 and EAR-1216301. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.

Complex Faulting Across the Los Angeles Portion of the Pacific-North American Plate Boundary

NASA Technical Reports Server (NTRS)

Donnellan, Andrea; Parker, Jay; Granat, Robert; Glasscae, Maggi; Lyzenga, Greg; Grant Ludwig, Lisa; Rundle, John

2011-01-01

We propose to observe seismically and tectonically active regions in northern and southern California using UAVSAR to support EarthScope activities. We will test the earthquake forecasting methodology developed by Rundle through NASA's QuakeSim project by observing regions indicated as having high probability for earthquakes in the near future (5-10 years). The UAVSAR flights will serve as a baseline for pre-earthquake activity. Should an earthquake occur during the course of this project, we will also be able to observe postseismic motions associated with the earthquakes.

Plate Boundary Observatory Infrastructure and Data Products in Education and Outreach

NASA Astrophysics Data System (ADS)

Eriksson, S. C.; Barbour, K.; Lee, E.

2005-12-01

As one of three major components of NSF's EarthScope program, the Plate Boundary Observatory (PBO) encourages the integration of research and education. Informing various communities about the current work of PBO and the scientific discoveries related to the use of this instrumentation has contributed to the success of PBO during the first two years of the EarthScope project. UNAVCO(PBO), IRIS (USArray), and the EarthScope project office work together to integrate Education and Outreach (E&O) opportunities into a program that is greater than the sum of its parts and yet maintains the identity of each organization. Building and maintaining the PBO website, documenting and archiving activities of PBO, providing short courses for professional development of scientists using EarthScope data, and developing higher level data products with an appropriate educational framework are a few of the activities that provide both challenges and opportunities. The internet, particularly the World Wide Web, has become the primary tool for disseminating information to various audiences. The primary goals of the PBO website are to provide current information on the progress of GPS and Strainmeter facility construction; to provide access to different levels of data products; and to facilitate networking with and among scientists. Challenges for the PBO website include publishing current stories on installation projects while coordinating with field engineers on a regular basis; providing near to real time updates and maintaining quality assurance processes; and defining personnel requirements for a maintaining a dynamic website. Currently, archived photographs, web diaries, and numerous web highlights document PBO's success and provide a visual record of PBO's accomplishments and behind-the-scene activities over the last two years. The community charged PBO with increasing the number of scientists using its data. UNAVCO does this by providing short courses for professional development of young scientists and more established scientists broadening their research interests. In addition, collecting, manipulating, and aggregating real scientific data for classroom use is a current priority in science education. Educators want their students to use these data to draw conclusions following the logical processes characteristic of the scientific endeavor. Hence, PBO is a natural source of data for use in the classroom. Staff and community members are designing higher level data products for a variety of audiences in formal education (students and instructors in middle/high school, community colleges, undergraduate science majors and students in general science education, graduate students) and in informal education (museums, park information centers, science centers, and media. PBO is working on a chapter for the Earth Exploration Toolbox (http://serc.carleton.edu/eet/) for undergraduate general science education, and the Jules Verne Voyager will include a user-friendly interface and associated educational materials. Evaluation of the effectiveness of this entire program and of individual projects and products is a major undertaking. The multitude of tasks, integration of these tasks into a coherent program, and identification of resources for evaluation are both opportunities and challenges in helping build a program with measurable impact.

Detection of induced seismicity due to oil and gas extraction in the northern Gulf of Mexico, USA

NASA Astrophysics Data System (ADS)

Fadugba, Oluwaseun Idowu

Drilling operations and extraction of oil and gas (O&G) may lead to subsurface slumping or compression of sediments due to reduced vertical principal stress which may lead to small earthquakes at the drilling site. O&G extraction is common in the northern Gulf of Mexico (NGM) and only thirty-five earthquakes of magnitudes between 2.3 and 6.0 have been recorded in the area from 1974 to the present. The purpose of this research is to detect more earthquakes using stacks of seismic data from the Transportable USArray (TA) from 2011 to 2013, and determine the spatiotemporal relationship between the detected earthquakes and O&G extraction. Five new small offshore earthquakes, that may be associated with the offshore O&G production, have been detected in the data. Spatial correlation of the epicenters with offshore drilling sites shows that the earthquakes may be due to the O&G extraction.

Building A Collaborative And Distributed E&O Program For EarthScope

NASA Astrophysics Data System (ADS)

Hall-Wallace, M. K.; Boyd, T.; Richard, G.; Ellins, K.; Meertens, C.; Semken, S.; Taber, J.; Benthien, M.; Wald, L.; Marvinney, R.

2003-12-01

EarthScope's education and outreach (E&O) mission is to ensure that the EarthScope experiment creates as its legacy a public more knowledgeable and understanding of the scientific and societal contributions made by the EarthScope experiment and Earth science. It will fulfill this commitment by developing and disseminating programs and products that utilize the data, models, technology and discoveries of EarthScope. The EarthScope Education and Outreach Network (EON), consisting of local EON alliances, the EarthScope facilities, partner organizations and a coordinating office, will facilitate this E&O mission. The local EON alliances, which will vary in size and purpose to respond quickly and to meet the specific needs in a region, will carry out the bulk of the effort. Thus, EarthScope EON can provide customized services that engage culturally, economically and geographically diverse audiences at the national and local scales. The EarthScope facilities and research community will provide access to data, models, and visualization tools for educational purposes. Partnerships with other national and local science education and outreach programs at colleges, universities, research facilities and professional societies within the EarthScope community as well as relevant programs at museums and parks, state geologic surveys and emergency management agencies, and K-12 schools are critical to EON's success. These partnerships will allow EON to use existing resources, networks and expertise to gear up quickly and efficiently. As EON develops, it will reciprocate by contributing new resources and expertise to the partnerships that help improve public understanding of Earth systems overall and promote effective application of EarthScope discoveries. In this presentation, we will outline major programs and products envisioned for EarthScope, plans for evaluating those programs locally and nationally, and mechanisms for collaborating with existing E&O programs.

Resistivity Image from 2D Inversion of Magnetotelluric Data in the Northern Cascadia Subduction Zone (United States)

NASA Astrophysics Data System (ADS)

Gultom, F. B.; Niasari, S. W.; Hartantyo, E.

2018-04-01

Cascadia Subduction Zone (CSZ) lies between Pacific margin and North America plate. The purpose of this research is to identify the CSZ along Oregon, Idaho, Wyoming from conductivity (σ) contrast in the subsurface by using the magnetotelluric (MT) method. MT is an electromagnetic method that use frequency between 10-4 Hz and 104 Hz. We obtained the MT data from the EarthScope USArray in the form of EDI-File (five components of the electromagnetic field). We analyzed the MT data using phase tensor and modeled the data using 2D inversion. From the phase tensor analysis, the 3D data dominated the eastern regions. Global data misfit is 6,88, where WYI18 (close to Yellowstone) contributes misfit of 29,3. This means that the model response does not fit the data, which implies the data is not fully 2D. The 2D inversion results are found high resistivity anomalies (more than 500 ohm.m) at shallow depth beneath Oregon and Wyoming, which coresspond to high density anomalies. This high resistivity anomalies might correspond to the north American plate. Thus, it can be concluded that 2D inversion model can be used for most 3D MT data to illustrate the resistivity distribution in the Cascadia Subduction Zone.

Wave Gradiometry for the Central U.S

NASA Astrophysics Data System (ADS)

liu, Y.; Holt, W. E.

2013-12-01

Wave gradiometry is a new technique utilizing the shape of seismic wave fields captured by USArray transportable stations to determine fundamental wave propagation characteristics. The horizontal and vertical wave displacements, spatial gradients and time derivatives of displacement are linearly linked by two coefficients which can be used to infer wave slowness, back azimuth, radiation pattern and geometrical spreading. The reducing velocity method from Langston [2007] is applied to pre-process our data. Spatial gradients of the shifted displacement fields are estimated using bi-cubic splines [Beavan and Haines, 2001]. Using singular value decomposition, the spatial gradients are then inverted to iteratively solve for wave parameters mentioned above. Numerical experiments with synthetic data sets provided by Princeton University's Neal Real Time Global Seismicity Portal are conducted to test the algorithm stability and evaluate errors. Our results based on real records in the central U.S. show that, the average Rayleigh wave phase velocity ranges from 3.8 to 4.2 km/s for periods from 60-125s, and 3.6 to 4.0 km/s for periods from 25-60s, which is consistent with earth model. Geometrical spreading and radiation pattern show similar features between different frequency bands. Azimuth variations are partially correlated with phase velocity change. Finally, we calculated waveform amplitude and spatial gradient uncertainties to determine formal errors in the estimated wave parameters. Further effort will be put into calculating shear wave velocity structure with respect to depth in the studied area. The wave gradiometry method is now being employed across the USArray using real observations and results obtained to date are for stations in eastern portion of the U.S. Rayleigh wave phase velocity derived from Aug, 20th, 2011 Vanuatu earthquake for periods from 100 - 125 s.

Upside-Down Subduction of the Farallon Slab and the Origin of Yellowstone Volcanism from Finite-Frequency Tomography of USArray Receiver Functions

NASA Astrophysics Data System (ADS)

Zhou, Y.

2017-12-01

The origin of the Yellowstone and Snake River Plain volcanic track stretching over 600 km from Northwest Wyoming to the Idaho-Oregon border has been strongly debated. The most widely accepted interpretation involves the North America plate moving over a stationary narrow plume of hot materials rising up from the lowermost mantle. The plume model successfully explains the age-progressive volcanic track and high ratios of Helium-3/Helium-4 isotope observed in the basaltic volcanism but such a deep mantle plume has been long missing in seismic imaging. In this study, we apply a newly developed finite-frequency imaging method to receiver functions recorded at USArray stations to map the topography of two seismic discontinuities in the mantle, the 410-km and the 660-km discontinuity. The new images reveal a trail of anomalies within a previously imaged wavespeed slab gap and closely follow the surface volcanic track. This observation contradicts the plume model which requires anomalies at those depths to be confined in a narrow region directly beneath the present-day Yellowstone caldera. We propose an alternative interpretation of the Yellowstone volcanism as a result of an upside-down subduction of the stagnant oceanic Farallon plate in the Western US. This upside-down episode of subduction started about 16 million years ago in the mantle transition zone, where the younger slab beneath Oregon and Idaho penetrated the 660-km discontinuity, pulling down older stagnant slab. The upside-down subduction propagated north-westward and generated passive upwellings from the lower mantle, ascending through a water-rich mantle transition zone, producing melting and age-progressive volcanism.

Study of atmospheric gravity waves and infrasonic sources using the USArray Transportable Array pressure data

NASA Astrophysics Data System (ADS)

Hedlin, Michael; de Groot-Hedlin, Catherine; Hoffmann, Lars; Alexander, M. Joan; Stephan, Claudia

2016-04-01

The upgrade of the USArray Transportable Array (TA) with microbarometers and infrasound microphones has created an opportunity for a broad range of new studies of atmospheric sources and the large- and small-scale atmospheric structure through which signals from these events propagate. These studies are akin to early studies of seismic events and the Earth's interior structure that were made possible by the first seismic networks. In one early study with the new dataset we use the method of de Groot-Hedlin and Hedlin (2015) to recast the TA as a massive collection of 3-element arrays to detect and locate large infrasonic events. Over 2,000 events have been detected in 2013. The events cluster in highly active regions on land and offshore. Stratospherically ducted signals from some of these events have been recorded more than 2,000 km from the source and clearly show dispersion due to propagation through atmospheric gravity waves. Modeling of these signals has been used to test statistical models of atmospheric gravity waves. The network is also useful for making direct observations of gravity waves. We are currently studying TA and satellite observations of gravity waves from singular events to better understand how the waves near ground level relate to those observed aloft. We are also studying the long-term statistics of these waves from the beginning of 2010 through 2014. Early work using data bandpass filtered from 1-6 hr shows that both the TA and satellite data reveal highly active source regions, such as near the Great Lakes. de Groot-Hedlin and Hedlin, 2015, A method for detecting and locating geophysical events using clusters of arrays, Geophysical Journal International, v203, p960-971, doi: 10.1093/gji/ggv345.

Determination of Rayleigh wave ellipticity across the Earthscope Transportable Array using single-station and array-based processing of ambient seismic noise

NASA Astrophysics Data System (ADS)

Workman, Eli; Lin, Fan-Chi; Koper, Keith D.

2017-01-01

We present a single station method for the determination of Rayleigh wave ellipticity, or Rayleigh wave horizontal to vertical amplitude ratio (H/V) using Frequency Dependent Polarization Analysis (FDPA). This procedure uses singular value decomposition of 3-by-3 spectral covariance matrices over 1-hr time windows to determine properties of the ambient seismic noise field such as particle motion and dominant wave-type. In FPDA, if the noise is mostly dominated by a primary singular value and the phase difference is roughly 90° between the major horizontal axis and the vertical axis of the corresponding singular vector, we infer that Rayleigh waves are dominant and measure an H/V ratio for that hour and frequency bin. We perform this analysis for all available data from the Earthscope Transportable Array between 2004 and 2014. We compare the observed Rayleigh wave H/V ratios with those previously measured by multicomponent, multistation noise cross-correlation (NCC), as well as classical noise spectrum H/V ratio analysis (NSHV). At 8 s the results from all three methods agree, suggesting that the ambient seismic noise field is Rayleigh wave dominated. Between 10 and 30 s, while the general pattern agrees well, the results from FDPA and NSHV are persistently slightly higher (˜2 per cent) and significantly higher (>20 per cent), respectively, than results from the array-based NCC. This is likely caused by contamination from other wave types (i.e. Love waves, body waves, and tilt noise) in the single station methods, but it could also reflect a small, persistent error in NCC. Additionally, we find that the single station method has difficulty retrieving robust Rayleigh wave H/V ratios within major sedimentary basins, such as the Williston Basin and Mississippi Embayment, where the noise field is likely dominated by reverberating Love waves and tilt noise.

Transformation of MT Resistivity Sections into Geologically Meaningful Images

NASA Astrophysics Data System (ADS)

Park, S. K.

2004-05-01

Earthscope offers an unprecedented opportunity for interdisciplinary studies of North America. In addition to a continent-wide seismic study, it includes the acquisition of magnetotelluric (MT) data at many of the Bigfoot array sites. Earthscope will thus provide a uniform 3-D MT survey over regional scales when completed. MT interpreters will be able to include 3-D regional effects in their models for the first time whether they are interpreting local studies. However, the full value of the interdisciplinary nature of Earthscope will be realized only if MT sections and maps are useful to other earth scientists. The standard final product from any 2-D or 3-D MT interpretation is a spatial distribution of electrical resistivity. Inference of the physicochemical state from bulk resistivity is complicated because a variety of factors influence the property including temperature, intrinsic conduction of silicates, and small amounts of interconnected conducting materials (e.g., graphite, metallic minerals, partial melt, fluid). Here, I use petrophysical measurements and a petrological model to transform a resistivity section into cross sections of temperature and partial melt fraction in the mantle beneath the Sierra Nevada. In this manner, I am able to separate the contributions of increasing temperature and melt fraction to the bulk resistivity. Predicted melt fractions match observations from xenoliths relatively well but temperatures are systematically 200C higher than those observed. A small amount of dissolved hydrogen (~70 ppm H/Si) lowers the predicted temperatures to match those from the xenoliths, however. I conclude that while this transformation is a simple first step based on many assumptions, initial results are promising.

Volcanic tremor and plume height hysteresis from Pavlof Volcano, Alaska

NASA Astrophysics Data System (ADS)

Fee, David; Haney, Matthew M.; Matoza, Robin S.; Van Eaton, Alexa R.; Cervelli, Peter; Schneider, David J.; Iezzi, Alexandra M.

2017-01-01

The March 2016 eruption of Pavlof Volcano, Alaska, produced an ash plume that caused the cancellation of more than 100 flights in North America. The eruption generated strong tremor that was recorded by seismic and remote low-frequency acoustic (infrasound) stations, including the EarthScope Transportable Array. The relationship between the tremor amplitudes and plume height changes considerably between the waxing and waning portions of the eruption. Similar hysteresis has been observed between seismic river noise and discharge during storms, suggesting that flow and erosional processes in both rivers and volcanoes can produce irreversible structural changes that are detectable in geophysical data. We propose that the time-varying relationship at Pavlof arose from changes in the tremor source related to volcanic vent erosion. This relationship may improve estimates of volcanic emissions and characterization of eruption size and intensity.

Travel-time Tomography of the Upper Mantle using Amphibious Array Seismic Data from the Cascadia Initiative and EarthScope

NASA Astrophysics Data System (ADS)

Cafferky, S.; Schmandt, B.

2013-12-01

Offshore and onshore broadband seismic data from the Cascadia Initiative and EarthScope provide a unique opportunity to image 3-D mantle structure continuously from a spreading ridge across a subduction zone and into continental back-arc provinces. Year one data from the Cascadia Initiative primarily covers the northern half of the Juan de Fuca plate and the Cascadia forearc and arc provinces. These new data are used in concert with previously collected onshore data for a travel-time tomography investigation of mantle structure. Measurement of relative teleseismic P travel times for land-based and ocean-bottom stations operating during year one was completed for 16 events using waveform cross-correlation, after bandpass filtering the data from 0.05 - 0.1 Hz with a second order Butterworth filter. Maps of travel-time delays show changing patterns with event azimuth suggesting that structural variations exist beneath the oceanic plate. The data from year one and prior onshore travel time measurements were used in a tomographic inversion for 3-D mantle P-velocity structure. Inversions conducted to date use ray paths determined by a 1-D velocity model. By meeting time we plan to present models using ray paths that are iteratively updated to account for 3-D structure. Additionally, we are testing the importance of corrections for sediment and crust thickness on imaging of mantle structure near the subduction zone. Low-velocities beneath the Juan de Fuca slab that were previously suggested by onshore data are further supported by our preliminary tomographic inversions using the amphibious array data.

Seismic Noise Characterization in the Northern Mississippi Embayment

NASA Astrophysics Data System (ADS)

Wiley, S.; Deshon, H. R.; Boyd, O. S.

2009-12-01

We present a study of seismic noise sources present within the northern Mississippi embayment near the New Madrid Seismic Zone (NMSZ). The northern embayment contains up to 1 km of unconsolidated coastal plain sediments overlying bedrock, making it an inherently noisy environment for seismic stations. The area is known to display high levels of cultural noise caused by agricultural activity, passing cars, trains, etc. We characterize continuous broadband seismic noise data recorded for the months of March through June 2009 at six stations operated by the Cooperative New Madrid Seismic Network. We looked at a single horizontal component of data during nighttime hours, defined as 6:15PM to 5:45AM Central Standard Time, which we determined to be the lowest amplitude period of noise for the region. Hourly median amplitudes were compared to daily average wind speeds downloaded from the National Oceanic and Atmospheric Administration. We find a correlation between time periods of increased noise and days with high wind speeds, suggesting that wind is likely a prevalent source of seismic noise in the area. The effects of wind on seismic recordings may result from wind induced tree root movement which causes ground motion to be recorded at the vaults located ~3m below ground. Automated studies utilizing the local network or the EarthScope Transportable Array, scheduled to arrive in the area in 2010-11, should expect to encounter wind induced noise fluctuations and must account for this in their analysis.

Seismic evidence for mantle suture and a collisional origin for the Canadian Cordillera

NASA Astrophysics Data System (ADS)

Chen, Y.; Gu, Y. J.; Currie, C. A.; Johnston, S. T.; Hung, S. H.; Schaeffer, A. J.; Audet, P.

2017-12-01

The North American Cordillera is a Phanerozoic orogenic belt that extends from Mexico to Alaska. Its eastern boundary is marked by pronounced changes in geophysical observations (e.g., mantle seismic velocity, surface heat flow, and effective elastic thickness) indicating a steep structural gradient beneath the Cordilleran foreland and the adjacent North American Craton. Seismological constraints on this boundary zone have been highly uneven: on the one hand, the knowledge of subsurface structures of the US Cordillera has been greatly enhanced by the USArray; on the other hand, detailed surveys of the northern counterpart, the Canadian Cordillera, are limited due to relatively sparse broadband data coverage. Questions pertaining to where and how Cordillera-Craton transition occurs in the upper mantle remain debated. Here, we utilize new teleseismic travel-time data from recently deployed networks in the Alberta foreland basin and nearby USArray stations and invert for mantle seismic velocities using finite-frequency tomography. The resulting high-resolution 3D model shows a dramatic increase in lithosphere thickness (>200 km) from the Cordillera to Craton. Additionally, independent calculations of mantle temperature from P (4.3%) and S (7.0%) velocity contrasts yield a consistent eastward 200-300 °C decrease at 150 km depth. We attribute the sharp structural and temperature/velocity gradients to the Cordillera-Craton boundary (CCB) established since at least the Late Cretaceous (ca. 100 Ma). The CCB dips steeply to the west beneath a carbonate belt that delineates a cryptic orogenic suture near the southern Rocky Mountain Trench, which provides strong evidence for an upper mantle suture between North America and an allochthonous Cordillera. The westward-dipping CCB may be a preserved structure associated with partial subduction of the leading edge of the North American Craton during its terminal collision with a microcontinent (Cordillera); this would require a strong craton lithosphere in order to preserve the observed geometry for >100 Ma. In this case, the earlier interpretation of the Cordillera as an accretionary orogen characterized by thin-skinned thrusting of exotic terranes over an intact North American basement and oceanward-tapering lithospheric mantle, is deemed unlikely.

Sutures, Sinkers, Shear zones and Sills: Cryptic Targets and Explicit Strategies for EARTHSCOPE FlexArray in the East

NASA Astrophysics Data System (ADS)

Brown, L. D.

2006-05-01

Given the 3D framework represented by EarthScope's USArray as it scans eastward, the strategic challenge falls to defining cost-effective deployments of FlexArray to address specific lithospheric targets. Previous deep geophysical surveys (e.g. COCORP, USGS, GLIMPCE, et al.) provide guidance not only in framing the geological issues involved, but in designing field experiments that overcome the limitations of previous work. Opportunities highlighted by these precursor studies include: a) Collisional sutures (e.g. Brunswick Anomaly/Suwannee terrane) which lie buried beneath overthrust terranes/ younger sedimentary covers. Signal penetration in previous controlled source surveys has been insufficient. High resolution passive surveys designed to map intralithospheric detachments, Moho, and mantle subduction scars is needed to validate the extrapolations of the existing upper crustal information; b) Intracratonic basins and domes (e.g. Michigan Basin, Adirondack Dome) are perhaps the greatest geological mystery hosted in the east. Previous geophysical studies have lacked the resolution or penetration needed to identify the buoyancy drivers presumed to be responsible for such structures. It is likely that these drivers lie in the upper mantle and will require detailed velocity imaging to recognized. c) Distributed shear fabrics are a defining characteristic of the deep crust in many deformation zones (e.g. Grenville Front). Detailed mapping of crustal anisotropy associated with such shear zones should help delineate ductile flow directions associated with the orogenies that accreted the eastern U.S. 3 component, 3D active+passive surveys are needed to obtain definitive remote measures of such vector characteristics in the deep crust. d) Extensive reflectors in the central U.S. may mark important buried Precambrian basins and/or sill complexes. If the latter, the magmatic roots of those systems remain unrecognized, as does their volumetric contribution to crustal growth. 3C expanding spreads to resolve lithology in the upper crust, coupled with passive imaging of potential mantle sources, are needed to evaluate the role of these sequences in mid Proterozoic continental evolution. Effective experiments must build upon existing data, be strategic in the selection of the various FlexArray tools available, and link operationally with the Bigfoot deployments in an appropriately staged fashion.

A Look at the Future of Controlled-Source Seismology

NASA Astrophysics Data System (ADS)

Keller, G. R.; Klemperer, S.; Hole, J.; Snelson, C.

2008-12-01

Facilities like EarthScope and IRIS/PASSCAL offer a framework in which to re-assess the role of our highest- resolution geophysical tool, controlled-source seismology. This tool is effective in near surface studies that focus on the upper 100 m of the crust to studies that focus on Moho structure and the lithospheric mantle. IRIS has now existed for over two decades and has transformed the way in which passive-source seismology in particular is carried out. Progress over these two decades has led to major discoveries about continental architecture and evolution through the development of three-dimensional images of the upper mantle and lithosphere. Simultaneously the hydrocarbon exploration industry has mapped increasingly large fractions of our sedimentary basins in three-dimensions and at unprecedented resolution and fidelity. Thanks to the additional instruments in the EarthScope facility, a clear scientific need and opportunity exists to map, at similar resolution, all of the crust - the igneous/metamorphic basement, the non-petroliferous basins that contain the record of continental evolution, and the seismogenic faults and active volcanoes that are the principal natural hazards we face. Controlled-source seismology remains the fundamental technology behind exploration for all fossil fuels and many water resources, and as such is a multi-billion-dollar industry centered in the USA. Academic scientists are leaders in developing the algorithms to process the most advanced industry data, but lack the academic data sets to which to apply this technology. University and government controlled-source seismologists, and their students who will populate the exploration industry, are increasingly divorced from that industry by their reliance on sparse spatial recording of usually only a single-component of the wavefield, generated by even sparser seismic sources. However, if we can find the resources, the technology now exists to provide seismic images of immense scientific and societal value that play a key role in fulfilling the ambitious missions of EarthScope and other NSF programs, as well as, those of agencies such as the U. S. Geological Survey and Department of Energy. US controlled-source community has self-organized to form an IASPEI U.S. National Committee on Controlled-Source Seismology to facilitate communication and to present and pursue the fundamental needs to sustain this scientific community as a resource for all earth scientists.

Volcanic tremor and plume height hysteresis from Pavlof Volcano, Alaska.

PubMed

Fee, David; Haney, Matthew M; Matoza, Robin S; Van Eaton, Alexa R; Cervelli, Peter; Schneider, David J; Iezzi, Alexandra M

2017-01-06

The March 2016 eruption of Pavlof Volcano, Alaska, produced an ash plume that caused the cancellation of more than 100 flights in North America. The eruption generated strong tremor that was recorded by seismic and remote low-frequency acoustic (infrasound) stations, including the EarthScope Transportable Array. The relationship between the tremor amplitudes and plume height changes considerably between the waxing and waning portions of the eruption. Similar hysteresis has been observed between seismic river noise and discharge during storms, suggesting that flow and erosional processes in both rivers and volcanoes can produce irreversible structural changes that are detectable in geophysical data. We propose that the time-varying relationship at Pavlof arose from changes in the tremor source related to volcanic vent erosion. This relationship may improve estimates of volcanic emissions and characterization of eruption size and intensity. Copyright © 2017, American Association for the Advancement of Science.

Integrating EarthScope Research and Education on a National Scale

NASA Astrophysics Data System (ADS)

Hall-Wallace, M. K.; Boyd, T.; Richard, G.; Ellins, K.; Meertens, C.; Semken, S.; Taber, J.; Benthien, M.; Wald, L.; Marvinney, R.

2002-12-01

EarthScope's education and outreach mission is to ensure the EarthScope experiment creates as its legacy a public more knowledgeable and understanding of the scientific and societal contributions made by the EarthScope experiment and Earth science. It will fulfill this commitment by developing and disseminating products that utilize the data, models, technology and discoveries of EarthScope and that support existing education and outreach programs. EarthScope EON will carry out educational activities ranging from research experiences for students in grades K-16 to professional development for technical professionals and educators in both formal (e.g. K-20 classrooms) and informal (e.g. museums and parks) venues. It will also provide a wide range of outreach activities from organizing town halls or other local meetings in advance of an instrument deployment, to developing radio, print and video materials that inform the public about the EarthScope experiment and discoveries. The EarthScope Education and Outreach Network (EON) will be facilitated and coordinated through a national center; however, the bulk of the effort will be distributed among local EON alliances of various sizes designed to respond quickly and to meet the specific needs in a region. This allows EarthScope EON to provide customized services that engage culturally, economically and geographically diverse audiences at the national and local scales. The network will be built through national and local partnerships with existing science education and outreach programs at colleges, universities, research facilities and professional societies within the EarthScope community as well as relevant programs at museums and parks, state geologic surveys and emergency management agencies, and K-12 schools. These partnerships will allow EON to use existing resources, networks and expertise to gear up quickly and efficiently. As EON develops, it will reciprocate by contributing new resources and expertise to the partnerships that help improve public understanding of Earth systems overall and promote effective application of EarthScope discoveries.

Education and Outreach at the Earthscope National Office: 2012 Update on Activities and Broader Impacts

NASA Astrophysics Data System (ADS)

Semken, S. C.; Arrowsmith, R.; Fouch, M. J.; Garnero, E. J.; Taylor, W. L.; Bohon, W.; Pacheco, H. A.; Schwab, P.; Baumback, D.; Pettis, L.; Colunga, J.; Robinson, S.; Dick, C.

2012-12-01

The EarthScope Program (www.earthscope.org) funded by the National Science Foundation fosters interdisciplinary exploration of the geologic structure and evolution of the North American continent by means of seismology, geodesy, magnetotellurics, in-situ fault-zone sampling, geochronology, and high-resolution topographic measurements. EarthScope scientific data and findings are transforming the study of Earth structure and processes throughout the planet. These data enhance the understanding and mitigation of hazards and inform environmental and economic applications of geoscience. The EarthScope Program also offers significant resources and opportunities for education and outreach (E&O) in the Earth system sciences. The EarthScope National Office (ESNO) at Arizona State University serves all EarthScope stakeholders, including researchers, educators, students, and the general public. ESNO continues to actively support and promote E&O with programmatic activities such as a regularly updated presence on the web and social media, newsletters, biannual national conferences, workshops for E&O providers and informal educators (interpreters), collaborative interaction with other Earth science organizations, continuing education for researchers, promotion of place-based education, and support for regional K-12 teacher professional-development programs led by EarthScope stakeholders. EarthScope E&O, coordinated by ESNO, leads the compilation and dissemination of the data, findings, and legacy of the epic EarthScope Program. In this presentation we offer updated reports and outcomes from ESNO E&O activities, including web and social-media upgrades, the Earth Science E&O Provider Summit for partnering organizations, the Central Appalachian Interpretive Workshop for informal Earth science educators, the U.S. Science and Engineering Fair, and collaborative efforts with partner organizations. The EarthScope National Office is supported by the National Science Foundation under grants EAR-1101100 and EAR-1216301. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.

Earthscope National Office Education and Outreach Program: 2014 Update on Broader-Impacts Activities and Outcomes

NASA Astrophysics Data System (ADS)

Semken, S. C.; Robinson, S.; Bohon, W.; Schwab, P.; Arrowsmith, R.; Garnero, E.; Pettis, L.; Baumback, D.; Dick, C.

2014-12-01

The EarthScope Program (www.earthscope.org), funded by the National Science Foundation, fosters interdisciplinary exploration of the geologic structure and evolution of the North American continent by means of geodesy, seismology, magnetotellurics, in-situ fault-zone sampling, geochronology, and high-resolution topographic measurements. EarthScope data, and the scientific findings they underpin, continue to revolutionize geoscientific research, enhance understanding and mitigation of geologic hazards, and bolster applications of geoscience in environmental management and sustainability. The EarthScope Program also produces and shares a wide range of resources and opportunities for education and outreach (E&O) in the Earth system sciences. The EarthScope National Office (ESNO) at Arizona State University serves all EarthScope stakeholders, including researchers, educators, students, and the general public. ESNO supports and promotes E&O through social media and the web, inSights newsletters and published articles, E&O workshops for informal educators (interpreters), an annual Speaker Series, assistance to grassroots K-12 STEM teacher professional development projects (typically led by EarthScope researchers), continuing education for researchers, collaborations with other Earth-science E&O providers, and biennial National Conferences. The EarthScope E&O program at ESNO, now in its final year at Arizona State University, leads and supports wide dissemination of the data, findings, and legacy of EarthScope. Significant activities in 2014 include an Interpretive Workshop in Alaska; the US Science and Engineering Festival; the Decade Symposium in Washington, DC; the Great ShakeOut; local and regional outreach; and a continued strong and exemplary E&O presence online. The EarthScope National Office is supported by the National Science Foundation under grants EAR-1101100 and EAR-1216301. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.

EarthScope National Office (ESNO) Education and Outreach Program and its Broader Impacts: 2015 Update and Handoff to the Next ESNO

NASA Astrophysics Data System (ADS)

Semken, S. C.; Robinson, S.; Bohon, W.; Arrowsmith, R.; Garnero, E.; Baumback, D.; Boot, K. E.; Dick, C.

2015-12-01

The EarthScope Program (www.earthscope.org), funded by the National Science Foundation, fosters interdisciplinary exploration of the geologic structure and evolution of the North American continent by means of geodesy, seismology, magnetotellurics, in-situ fault-zone sampling, geochronology, and high-resolution topographic measurements. Data and scientific findings from EarthScope are impacting and revolutionizing wide areas of geoscientific research, the understanding and mitigation of geologic hazards, and applications of geoscience to environmental sustainability. The EarthScope Program also produces and disseminates resources and programs for education and outreach (E&O) in the Earth system sciences. The EarthScope National Office (ESNO), operated by Arizona State University from 2011 to 2015, serves all EarthScope stakeholders, including researchers, educators, students, and the general public. ESNO supports and promotes E&O through social media and the web, inSights newsletters and published articles, E&O workshops for informal educators (interpreters), an annual Speaker Series, assistance to K-12 STEM teacher professional development projects led by EarthScope researchers, continuing education for researchers, collaborations with other Earth-science E&O providers, and a biennial National Meeting. Significant activities during the final year of ESNO at ASU included the EarthScope National Meeting in Vermont; Native Science professional-development workshops for Native American teachers in Arizona and Minnesota; a sustained E&O presence online; and preparation for the transition of ESNO from ASU to the next host institution. The EarthScope National Office is supported by the National Science Foundation under grants EAR-1101100 and EAR-1216301. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.

Interstation phase speed and amplitude measurements of surface waves with nonlinear waveform fitting: application to USArray

NASA Astrophysics Data System (ADS)

Hamada, K.; Yoshizawa, K.

2015-09-01

A new method of fully nonlinear waveform fitting to measure interstation phase speeds and amplitude ratios is developed and applied to USArray. The Neighbourhood Algorithm is used as a global optimizer, which efficiently searches for model parameters that fit two observed waveforms on a common great-circle path by modulating the phase and amplitude terms of the fundamental-mode surface waves. We introduce the reliability parameter that represents how well the waveforms at two stations can be fitted in a time-frequency domain, which is used as a data selection criterion. The method is applied to observed waveforms of USArray for seismic events in the period from 2007 to 2010 with moment magnitude greater than 6.0. We collect a large number of phase speed data (about 75 000 for Rayleigh and 20 000 for Love) and amplitude ratio data (about 15 000 for Rayleigh waves) in a period range from 30 to 130 s. The majority of the interstation distances of measured dispersion data is less than 1000 km, which is much shorter than the typical average path-length of the conventional single-station measurements for source-receiver pairs. The phase speed models for Rayleigh and Love waves show good correlations on large scales with the recent tomographic maps derived from different approaches for phase speed mapping; for example, significant slow anomalies in volcanic regions in the western Unites States and fast anomalies in the cratonic region. Local-scale phase speed anomalies corresponding to the major tectonic features in the western United States, such as Snake River Plains, Basin and Range, Colorado Plateau and Rio Grande Rift have also been identified clearly in the phase speed models. The short-path information derived from our interstation measurements helps to increase the achievable horizontal resolution. We have also performed joint inversions for phase speed maps using the measured phase and amplitude ratio data of vertical component Rayleigh waves. These maps exhibit better recovery of phase speed perturbations, particularly where the strong lateral velocity gradient exists in which the effects of elastic focussing can be significant; that is, the Yellowstone hotspot, Snake River Plains, and Rio Grande Rift. The enhanced resolution of the phase speed models derived from the interstation phase and amplitude measurements will be of use for the better seismological constraint on the lithospheric structure, in combination with dense broad-band seismic arrays.

Engaging the Geodetic and Geoscience Communities in EarthScope Education and Outreach

NASA Astrophysics Data System (ADS)

Charlevoix, D. J.; Berg, M.; Morris, A. R.; Olds, S. E.

2013-12-01

UNAVCO is NSF's geodetic facility and operates as a university-governed consortium dedicated to facilitating geoscience research and education, including the support of EarthScope. The Education and Community Engagement program at UNAVCO provides support for broader impacts both externally to the broader University and EarthScope community as well as internally to the UNAVCO. During the first 10 years of EarthScope UNAVCO has engaged in outreach and education activities across the EarthScope footprint ranging from outreach to formal and informal educators and interpreters, to technical training for university faculty and researchers. UNAVCO works jointly with the EarthScope National Office and IRIS while simultaneously maintaining and developing an independent engagement and education program. UNAVCO provides training in the form of technical short courses to researchers including graduate students and early-career professionals, and conducts educational workshops for K-12 educators. A suite of educational materials focused on the integration of EarthScope data into curriculum materials is available from UNAVCO and will soon expand the undergraduate offerings to include a broader suite of geodesy applications activities for undergraduate students. UNAVCO provides outreach materials and in support of EarthScope including summaries of research project and campaign highlights, science snapshots featuring summaries of scientific advancements made possible by UNAVCO services and non-technical communications via social media. UNAVCO also provides undergraduate students exposure to EarthScope science research participation in a year-long research internship managed by UNAVCO (Research Experiences in Solid Earth Science for Students - RESESS).

Developing Federated Services within Seismology: IRIS' involvement in the CoopEUS Project

NASA Astrophysics Data System (ADS)

Ahern, T. K.; Trabant, C. M.; Stults, M.

2014-12-01

As a founding member of the CoopEUS initiative, IRIS Data Services has partnered with five data centers in Europe and the UC Berkeley (NCEDC) in the US to implement internationally standardized web services to access seismological data using identical methodologies. The International Federation of Digital Seismograph Networks (FDSN) holds commission status within IASPEI/IUGG and as such is the international body that governs data exchange formats and access protocols within seismology. The CoopEUS project involves IRIS and UNAVCO as part of the EarthScope project and the European collaborators are all members of the European Plate Observing System (EPOS). CoopEUS includes one work package that attempts to coordinate data access between EarthScope and EPOS facilities. IRIS has worked with its partners in the FDSN to develop and adopt three key international service standards within seismology. These include 1) fdsn-dataselect, a service that returns time series data in a variety of standard formats, 2) fdsn-station, a service that returns related metadata about a seismic station in stationXML format, and 3) fdsn-event, a service that returns information about earthquakes and other seismic events in QuakeML format. Currently the 5 European data centers supporting these services include the ORFEUS Data Centre in the Netherlands, the GFZ German Research Centre for Geosciences in Potsdam, Germany, ETH Zurich in Switzerland, INGV in Rome, Italy, and the RESIF Data Centre in Grenoble France. Presently these seven centres can all be accessed using standardized web services with identical service calls and returns results in standardized ways. IRIS is developing an IRIS federator that will allow a client to seamlessly access information across the federated centers. Details and current status of the IRIS Federator will be presented.

Low-latency high-rate GPS data streams from the EarthScope Plate Boundary Observatory

NASA Astrophysics Data System (ADS)

Anderson, G.; Borsa, A.; Jackson, M.; Stark, K.

2008-05-01

Real-time processing of high rate GPS data can give precise (e.g., 5-10 mm for data recorded once per second) recordings of rapid volcanic and seismic deformation. These time series now provide an emerging tool for seismic, volcanic, and tsunami geodesy and early warning applications. UNAVCO, as part of the EarthScope Plate Boundary Observatory project, has developed the UStream system to provide streaming GPS data from some PBO and other UNAVCO-operated GPS stations. UStream is based on the Ntrip standard, a widely used protocol for streaming GNSS data over the Internet. Remote GPS stations provide a stream of BINEX data at 1 sample/sec to an Ntrip server at UNAVCO's Boulder offices, while simultaneously recording data locally in the event of communications failure. Once in Boulder, the data fork into three output streams: BINEX files stored at UNAVCO and streams of data in BINEX and RTCM 2.3 format. These streams flow to an Ntrip broadcaster that distributes data to Ntrip clients, which can be anything from low-latency processing systems to external data archiving systems. Current development efforts are geared toward providing data in RTCM 3.x format. This system is now operating in a public beta test mode, with data available from over 55 PBO and Nucleus GPS stations across the western United States. Data latencies from stations operating on mobile telephone communications are under 1.1 seconds at 95% confidence, and data completeness is typically more than 95% barring transient communications disruptions. Data from the system are available under the terms of the draft UNAVCO streaming data usage policy. For further information, please visit http://rtgps.unavco.org or send e-mail to rtgps@unavco.org.

Seismicity of the Wabash Valley, Ste. Genevieve, and Rough Creek Graben Seismic Zones from the Earthscope Ozarks-Illinois-Indiana-Kentucky (OIINK) FlexArray Experiment

NASA Astrophysics Data System (ADS)

Shirley, Matthew Richard

I analyzed seismic data from the Ozarks-Illinois-Indiana-Kentucky (OIINK) seismic experiment that operated in eastern Missouri, southern Illinois, southern Indiana, and Kentucky from July 2012 through March 2015. A product of this analysis is a new catalog of earthquake locations and magnitudes for small-magnitude local events during this study period. The analysis included a pilot study involving detailed manual analysis of all events in a ten-day test period and determination of the best parameters for a suite of automated detection and location programs. I eliminated events that were not earthquakes (mostly quarry and surface mine blasts) from the output of the automated programs, and reprocessed the locations for the earthquakes with manually picked P- and S-wave arrivals. This catalog consists of earthquake locations, depths, and local magnitudes. The new catalog consists of 147 earthquake locations, including 19 located within the bounds of the OIINK array. Of these events, 16 were newly reported events, too small to be reported in the Center for Earthquake Research and Information (CERI) regional seismic network catalog. I compared the magnitudes reported by CERI for corresponding earthquakes to establish a magnitude calibration factor for all earthquakes recorded by the OIINK array. With the calibrated earthquake magnitudes, I incorporate the previous OIINK results from Yang et al. (2014) to create magnitude-frequency distributions for the seismic zones in the region alongside the magnitude-frequency distributions made from CERI data. This shows that Saint Genevieve and Wabash Valley seismic zones experience seismic activity at an order magnitude lower rate than the New Madrid seismic zone, and the Rough Creek Graben experiences seismic activity two orders of magnitude less frequently than New Madrid.

Quantifying uncertainties of seismic Bayesian inversion of Northern Great Plains

NASA Astrophysics Data System (ADS)

Gao, C.; Lekic, V.

2017-12-01

Elastic waves excited by earthquakes are the fundamental observations of the seismological studies. Seismologists measure information such as travel time, amplitude, and polarization to infer the properties of earthquake source, seismic wave propagation, and subsurface structure. Across numerous applications, seismic imaging has been able to take advantage of complimentary seismic observables to constrain profiles and lateral variations of Earth's elastic properties. Moreover, seismic imaging plays a unique role in multidisciplinary studies of geoscience by providing direct constraints on the unreachable interior of the Earth. Accurate quantification of uncertainties of inferences made from seismic observations is of paramount importance for interpreting seismic images and testing geological hypotheses. However, such quantification remains challenging and subjective due to the non-linearity and non-uniqueness of geophysical inverse problem. In this project, we apply a reverse jump Markov chain Monte Carlo (rjMcMC) algorithm for a transdimensional Bayesian inversion of continental lithosphere structure. Such inversion allows us to quantify the uncertainties of inversion results by inverting for an ensemble solution. It also yields an adaptive parameterization that enables simultaneous inversion of different elastic properties without imposing strong prior information on the relationship between them. We present retrieved profiles of shear velocity (Vs) and radial anisotropy in Northern Great Plains using measurements from USArray stations. We use both seismic surface wave dispersion and receiver function data due to their complementary constraints of lithosphere structure. Furthermore, we analyze the uncertainties of both individual and joint inversion of those two data types to quantify the benefit of doing joint inversion. As an application, we infer the variation of Moho depths and crustal layering across the northern Great Plains.

Joint inversion of seismic and gravity data for imaging seismic velocity structure of the crust and upper mantle beneath Utah, United States

NASA Astrophysics Data System (ADS)

Syracuse, E. M.; Zhang, H.; Maceira, M.

2017-10-01

We present a method for using any combination of body wave arrival time measurements, surface wave dispersion observations, and gravity data to simultaneously invert for three-dimensional P- and S-wave velocity models. The simultaneous use of disparate data types takes advantage of the differing sensitivities of each data type, resulting in a comprehensive and higher resolution three-dimensional geophysical model. In a case study for Utah, we combine body wave first arrivals mainly from the USArray Transportable Array, Rayleigh wave group and phase velocity dispersion data, and Bouguer gravity anomalies to invert for crustal and upper mantle structure of the region. Results show clear delineations, visible in both P- and S-wave velocities, between the three main tectonic provinces in the region. Without the inclusion of the surface wave and gravity constraints, these delineations are less clear, particularly for S-wave velocities. Indeed, checkerboard tests confirm that the inclusion of the additional datasets dramatically improves S-wave velocity recovery, with more subtle improvements to P-wave velocity recovery, demonstrating the strength of the method in successfully recovering seismic velocity structure from multiple types of constraints.

Three Types of Earth's Inner Core Boundary

NASA Astrophysics Data System (ADS)

Tian, D.; Wen, L.

2017-12-01

The Earth's inner core boundary (ICB) is the site where the liquid outer core solidifies and the solid inner core grows. Thus, the fine-scale structure of the ICB is important for our understanding of the thermo-compositional state of the Earth's core. In this study, we collect a large set of seismic records with high-quality pre-critical PKiKP and PcP phase pairs, recorded by two dense seismic arrays, Hi-net in Japan and USArray in US. This dataset samples the ICB regions beneath East Asia, Mexico and the Bering Sea. We use differential travel times, amplitude ratios and waveform differences between PKiKP and PcP phases to constrain fine-scale structure of the ICB. The sampled ICB can be grouped into three types based on their seismic characteristics: (1) a simple ICB with a flat and sharp boundary, (2) a bumpy ICB with topographic height changes of 10 km, and (3) a localized mushy ICB with laterally varying thicknesses of 4-8 km. The laterally varying fine-scale structure of the ICB indicates existence of complex small-scale forces at the surface and a laterally varying solidification process of the inner core due to lateral variation of thermo-compositional condition near the ICB.

Imaging the complex Farallon subduction system with USArray derived joint inversion of body waves and surface waves

NASA Astrophysics Data System (ADS)

Porritt, R. W.; Allen, R. M.; Pollitz, F. F.; Hung, S.

2012-12-01

The 150 million year history of subduction of the Farallon plate is being well elucidated by the passage of USArray. In this study, we use body wave relative delay times to generate independent P, SV, and SH relative velocity models for the USArray footprint. In addition, we use Rayleigh wave phase velocities derived from teleseismic earthquakes and ambient seismic noise to constrain the lithospheric structure where body waves have limited crossing ray information to form the SV-joint velocity model. The model volume contains a complex series of high velocities mostly along a planar front representing the remnants of the Farallon plate system. This feature has significant lateral and radial extent; beginning off the western coast of the US and terminating east of the model resolution, which goes to the Mississippi river. The bottom of the slab is well imaged through the mantle transition zone to at least 1000km. However, low velocity anomalies within this plane show the slab is far from a continuous sheet. Low velocities break up the slab into several major provinces, relating to different ages of orogens and an episode of flat slab subduction. Additionally, high velocities are often imaged well above the trace of the top of the slab with similar anomaly amplitude and dip as the main slab. While many of these anomalies have been interpreted as mantle drips, the similarity to the slab suggests a possible subduction origin for the features. However, the relatively shallow depths of these features require some mechanism of differentiation to develop neutral buoyancy. The prevalence of these high velocities, such as the Siletzia Curtain, Isabella Anomaly, Nevada Anomaly, and a newly imaged feature under southwest Texas, suggests a differentiation mechanism is fairly common among plates subducting under North America allowing for the observation of widespread shallow high velocity anomalies.

EarthChem and SESAR: Data Resources and Interoperability for EarthScope Cyberinfrastructure

NASA Astrophysics Data System (ADS)

Lehnert, K. A.; Walker, D.; Block, K.; Vinay, S.; Ash, J.

2008-12-01

Data management within the EarthScope Cyberinfrastructure needs to pursue two goals in order to advance and maximize the broad scientific application and impact of the large volumes of observational data acquired by EarthScope facilities: (a) to provide access to all data acquired by EarthScope facilities, and to promote their use by broad audiences, and (b) to facilitate discovery of, access to, and integration of multi-disciplinary data sets that complement EarthScope data in support of EarthScope science. EarthChem and SESAR, the System for Earth Sample Registration, are two projects within the Geoinformatics for Geochemistry program that offer resources for EarthScope CI. EarthChem operates a data portal that currently provides access to >13 million analytical values for >600,000 samples, more than half of which are from North America, including data from the USGS and all data from the NAVDAT database, a web-accessible repository for age, chemical and isotopic data from Mesozoic and younger igneous rocks in western North America. The new EarthChem GEOCHRON database will house data collected in association with GeoEarthScope, storing and serving geochronological data submitted by participating facilities. The EarthChem Deep Lithosphere Dataset is a compilation of petrological data for mantle xenoliths, initiated in collaboration with GeoFrame to complement geophysical endeavors within EarthScope science. The EarthChem Geochemical Resource Library provides a home for geochemical and petrological data products and data sets. Parts of the digital data in EarthScope CI refer to physical samples such as drill cores, igneous rocks, or water and gas samples, collected, for example, by SAFOD or by EarthScope science projects and acquired through lab-based analysis. Management of sample-based data requires the use of global unique identifiers for samples, so that distributed data for individual samples generated in different labs and published in different papers can be unambiguously linked and integrated. SESAR operates a registry for Earth samples that assigns and administers the International GeoSample Numbers (IGSN) as a global unique identifier for samples. Registration of EarthScope samples with SESAR and use of the IGSN will ensure their unique identification in publications and data systems, thus facilitating interoperability among sample-based data relevant to EarthScope CI and globally. It will also make these samples visible to global audiences via the SESAR Global Sample Catalog.

Long period seismic noise modulated by atmospheric tides

NASA Astrophysics Data System (ADS)

Custódio, Susana; Helffrich, George

2016-04-01

The amplitudes of long-period (LP) seismic noise often exhibit a daily modulation, which is particularly visible on data recorded by temporary stations and horizontal components. These daily variations of the LP noise have been associated with temperature fluctuations. Temperature has been suggested to affect the noise recorded by seismometers by means of thermal convection around the sensor or by causing thermally induced tilts. Recently, we observed a semi-diurnal (12.0 hr) modulation of LP seismic noise amplitudes in seismometers in Portugal, SW Europe. This modulation was associated with the variation of atmospheric pressure, the only environmental signal to display a dominant 12-hr periodicity (at some locations). In this presentation we will present an analysis of this semi-diurnal modulation of long-period seismic noise. We show that the modulation: 1) is not instrument dependent, being recorded in a variety of sensors; 2) is observed in stations in mainland Portugal, Madeira island (N Atlantic), Florida (USA) and Mozambique, where it is strongest; 3) is seen only at a minority of sites without a clear geographical association, thus appearing to be strongly site-dependent; 5) is stronger during the Summer than during the Winter; and 6) is more clearly seen on vertical components. We will use data from the Transportable Array (EarthScope, USA) to investigate the admittance between LP seismic noise variations and co-located atmospheric pressure measurements.

New Constraints on Upper Mantle Structure Underlying the Diamondiferous Central Slave Craton, Canada, from Teleseismic Body Wave Tomography

NASA Astrophysics Data System (ADS)

Esteve, C.; Schaeffer, A. J.; Audet, P.

2017-12-01

Over the past number of decades, the Slave Craton (Canada) has been extensively studied for its diamondiferous kimberlites. Not only are diamonds a valuable resource, but their kimberlitic host rocks provide an otherwise unique direct source of information on the deep upper mantle (and potentially transition zone). Many of the Canadian Diamond mines are located within the Slave Craton. As a result of the propensity for diamondiferous kimberlites, it is imperative to probe the deep mantle structure beneath the Slave Craton. This work is further motivated by the increase in high-quality broadband seismic data across the Northern Canadian Cordillera over the past decade. To this end we have generated a P and S body wave tomography model of the Slave Craton and its surroundings. Furthermore, tomographic inversion techniques are growing ever more capable of producing high resolution Earth models which capture detailed structure and dynamics across a range of scale lengths. Here, we present preliminary results on the structure of the upper mantle underlying the Slave Craton. These results are generated using data from eight different seismic networks such as the Canadian National Seismic Network (CNSN), Yukon Northwest Seismic Network (YNSN), older Portable Observatories for Lithospheric Analysis and Reseach Investigating Seismicity (POLARIS), Regional Alberta Observatory for Earthquake Studies Network (RV), USArray Transportable Array (TA), older Canadian Northwest Experiment (CANOE), Batholith Broadband (XY) and the Yukon Observatory (YO). This regional model brings new insights about the upper mantle structure beneath the Slave Craton, Canada.

Monitoring Instrument Performance in Regional Broadband Seismic Network Using Ambient Seismic Noise

NASA Astrophysics Data System (ADS)

Ye, F.; Lyu, S.; Lin, J.

2017-12-01

In the past ten years, the number of seismic stations has increased significantly, and regional seismic networks with advanced technology have been gradually developed all over the world. The resulting broadband data help to improve the seismological research. It is important to monitor the performance of broadband instruments in a new network in a long period of time to ensure the accuracy of seismic records. Here, we propose a method that uses ambient noise data in the period range 5-25 s to monitor instrument performance and check data quality in situ. The method is based on an analysis of amplitude and phase index parameters calculated from pairwise cross-correlations of three stations, which provides multiple references for reliable error estimates. Index parameters calculated daily during a two-year observation period are evaluated to identify stations with instrument response errors in near real time. During data processing, initial instrument responses are used in place of available instrument responses to simulate instrument response errors, which are then used to verify our results. We also examine feasibility of the tailing noise using data from stations selected from USArray in different locations and analyze the possible instrumental errors resulting in time-shifts used to verify the method. Additionally, we show an application that effects of instrument response errors that experience pole-zeros variations on monitoring temporal variations in crustal properties appear statistically significant velocity perturbation larger than the standard deviation. The results indicate that monitoring seismic instrument performance helps eliminate data pollution before analysis begins.

Career in Feet-on Seismology

NASA Astrophysics Data System (ADS)

Van der Lee, S.

2011-12-01

My career award was for imaging the upper mantle beneath North America. The research proposed was timely because of Earthscope and novel because of the proposed simultaneous inversion of different types of seismic data as well as the inclusion of mineral physics data on the effects of volatiles on seismic properties of the mantle. This research has been challenging and fun and is still on-going. The educational component of my career award consists of feet-on and eyes-open learning of seismology through an educational kiosk and field trips to actual seismic stations. The kiosk and field station have both been growing over the years, as has the audience. I started with the field station in-doors, so it doubled as the kiosk along with a palmtop terminal. Groups of minority elementary school children would look at the mysterious hardware of the "field" station and then jump up and down so they could awe at the peaks in the graph on the palmtop screen that they created. This has evolved into a three-screen kiosk, of which one screen is a touch screen along with a demonstration seismometer. The field station is now in a goat shed near the epicenter of an actual 2010 earthquake inIllinois, which is soon to be replaced by a TA station of Earthscope. The audience has grown to entire grades of middle-school children and activities have evolved from jumping to team-experimentation and the derivation of amplitude-distance relationships following a collaborative curriculum. Addressing the questions in the session description: 1) Education is more fun and effective when one can work in a team with an enthusiastic educator. 2) My education activities are strongly related to my field of expertise but very loosely related to the research carried out with the career award. It appears that not the research outcomes are of interest to students, but instead the simplification and accessibility of the process of research that is of interest. 3) The education component of the career award has made me a better and more diversified teacher and I regularly involve graduate student into these education activities.

Velocity variations and uncertainty from transdimensional P-wave tomography of North America

NASA Astrophysics Data System (ADS)

Burdick, Scott; Lekić, Vedran

2017-05-01

High-resolution models of seismic velocity variations constructed using body-wave tomography inform the study of the origin, fate and thermochemical state of mantle domains. In order to reliably relate these variations to material properties including temperature, composition and volatile content, we must accurately retrieve both the patterns and amplitudes of variations and quantify the uncertainty associated with the estimates of each. For these reasons, we image the mantle beneath North America with P-wave traveltimes from USArray using a novel method for 3-D probabilistic body-wave tomography. The method uses a Transdimensional Hierarchical Bayesian framework with a reversible-jump Markov Chain Monte Carlo algorithm in order to generate an ensemble of possible velocity models. We analyse this ensemble solution to obtain the posterior probability distribution of velocities, thereby yielding error bars and enabling rigorous hypothesis testing. Overall, we determine that the average uncertainty (1σ) of compressional wave velocity estimates beneath North America is ∼0.25 per cent dVP/VP, increasing with proximity to complex structure and decreasing with depth. The addition of USArray data reduces the uncertainty beneath the Eastern US by over 50 per cent in the upper mantle and 25-40 per cent below the transition zone and ∼30 per cent throughout the mantle beneath the Western US. In the absence of damping and smoothing, we recover amplitudes of variations 10-80 per cent higher than a standard inversion approach. Accounting for differences in data coverage, we infer that the length scale of heterogeneity is ∼50 per cent longer at shallow depths beneath the continental platform than beneath tectonically active regions. We illustrate the model trade-off analysis for the Cascadia slab and the New Madrid Seismic Zone, where we find that smearing due to the limitations of the illumination is relatively minor.

Making geoscience education accessible for students who are blind and visually impaired

NASA Astrophysics Data System (ADS)

Charlevoix, D. J.; Berg, M.; Morris, A. R.; Olds, S. E.

2011-12-01

UNAVCO is NSF's geodetic facility and operates as a university-governed consortium dedicated to facilitating geoscience research and education, including the support of EarthScope. The Education and Community Engagement program at UNAVCO provides support for broader impacts both externally to the broader University and EarthScope community as well as internally to the UNAVCO. During the first 10 years of EarthScope UNAVCO has engaged in outreach and education activities across the EarthScope footprint ranging from outreach to formal and informal educators and interpreters, to technical training for university faculty and researchers. UNAVCO works jointly with the EarthScope National Office and IRIS while simultaneously maintaining and developing an independent engagement and education program. UNAVCO provides training in the form of technical short courses to researchers including graduate students and early-career professionals, and conducts educational workshops for K-12 educators. A suite of educational materials focused on the integration of EarthScope data into curriculum materials is available from UNAVCO and will soon expand the undergraduate offerings to include a broader suite of geodesy applications activities for undergraduate students. UNAVCO provides outreach materials and in support of EarthScope including summaries of research project and campaign highlights, science snapshots featuring summaries of scientific advancements made possible by UNAVCO services and non-technical communications via social media. UNAVCO also provides undergraduate students exposure to EarthScope science research participation in a year-long research internship managed by UNAVCO (Research Experiences in Solid Earth Science for Students - RESESS).

Multi-Mode 3D Kirchhoff Migration of Receiver Functions at Continental Scale With Applications to USArray

NASA Astrophysics Data System (ADS)

Millet, F.; Bodin, T.; Rondenay, S.

2017-12-01

The teleseismic scattered seismic wavefield contains valuable information about heterogeneities and discontinuities inside the Earth. By using fast Receiver Function (RF) migration techniques such as classic Common Conversion Point (CCP) stacks, one can easily interpret structural features down to a few hundred kilometers in the mantle. However, strong simplifying 1D assumptions limit the scope of these methods to structures that are relatively planar and sub-horizontal at local-to-regional scales, such as the Lithosphere-Asthenosphere Boundary and the Mantle Transition Zone discontinuities. Other more robust 2D and 2.5D methods rely on fewer assumptions but require considerable, sometime prohibitive, computation time. Following the ideas of Cheng (2017), we have implemented a simple fully 3D Prestack Kirchhoff RF migration scheme which uses the FM3D fast Eikonal solver to compute travel times and scattering angles. The method accounts for 3D elastic point scattering and includes free surface multiples, resulting in enhanced images of laterally varying dipping structures, such as subducted slabs. The method is tested for subduction structures using 2.5D synthetics generated with Raysum and 3D synthetics generated with specfem3D. Results show that dip angles, depths and lateral variations can be recovered almost perfectly. The approach is ideally suited for applications to dense regional datasets, including those collected across the Cascadia and Alaska subduction zones by USArray.

Infrasound Studies at the USArray (Invited)

NASA Astrophysics Data System (ADS)

de Groot-Hedlin, C. D.

2013-12-01

Many surface and atmospheric sources, both natural and anthropogenic, have generated infrasound signals that have been recorded on USArray transportable array (TA) seismometers at ranges up to thousands of kilometers. Such sources, including surface explosions, large bolides, mining events, and a space shuttle, have contributed to an understanding of infrasound propagation. We show examples of several atmospheric sources recorded at the TA. We first used USArray data to investigate infrasound signals from the space shuttle 'Atlantis'. Inclement weather in Florida forced the shuttle to land at Edwards Air Force Base in southern California on June 22, 2007, passing near three infrasound stations and several hundred seismic stations in northern Mexico, southern California, and Nevada. The high signal-to-noise ratio, broad receiver coverage, and Atlantis' positional information allowed us to test infrasound propagation modeling capabilities through the atmosphere to hundreds of kilometers range from the shuttle's path. Shadow zones and arrival times were predicted by tracing rays launched at right angles to the conical shock front surrounding the shuttle through a standard climatological model as well as a global ground to space model. Both models predict alternating regions of high and low ensonification to the NW, in line with observations. However, infrasound energy was detected tens of kilometers beyond the predicted zones of ensonification, possibly due to uncertainties in stratospheric wind speeds. The models also predict increasing waveform complexity with increasing distance, in line with observations. Several hundreds of broadband seismic stations in the U.S. Pacific Northwest recorded acoustic to seismic coupled signals from a large meteor that entered the atmosphere above northeastern Oregon on 19 February 2008. The travel times of the first arriving energy are consistent with a terminal explosion source model, suggesting that the large size of the explosion masked any signals associated with a continuous line source along its supersonic trajectory. Infrasound was detected at distances over 500 km from the source. A finite-difference time-domain algorithm that allows for propagation through a windy, viscous medium was developed to model signals from this source. We compare synthetics that have been computed using a G2S-ECMWF atmospheric model to signals recorded along an azimuth of 210 degrees from the source. The results show that the timing and the range extent of the direct, stratospherically ducted and thermospherically ducted acoustic branches are accurately predicted. However, estimates of absorption obtained from standard attenuation models predict much greater attenuation for thermospheric returns at frequencies greater than 0.1 Hz than is observed. We conclude that either the standard absorption model for the thermospheric is incorrect, or that thermospheric returns undergo non-linear propagation at very high altitude. In the former case, a better understanding of atmospheric absorption at high altitudes is required; in the latter, non-linear propagation modeling methods are needed to model infrasound propagation at thermospheric altitudes. Finally, we show infrasound signals recorded at TA barometers, generated by a small asteroid that entered Earth's atmosphere at distances between 6000-10000 km from the TA.

Introductory Earth science education by near real time animated visualization of seismic wave propagation across Transportable Array of USArray

NASA Astrophysics Data System (ADS)

Attanayake, J.; Ghosh, A.; Amosu, A.

2010-12-01

Students of this generation are markedly different from their predecessors because they grow up and learn in a world of visual technology populated by touch screens and smart boards. Recent studies have found that the attention span of university students whose medium of instruction is traditional teaching methods is roughly fifteen minutes and that there is a significant drop in the number of students paying attention over time in a lecture. On the other hand, when carefully segmented and learner-paced, animated visualizations can enhance the learning experience. Therefore, the instructors are faced with the difficult task of designing more complex teaching environments to improve learner productivity. We have developed an animated visualization of earthquake wave propagation across a generic transect of the Transportable Array of the USArray from a magnitude 6.9 event that occurred in the Gulf of California on August 3rd 2009. Despite the fact that the proto-type tool is built in MATLAB - one of the most popular programming environments among the seismology community, the movies can be run as a standalone stream with any built-in media player that supports .avi file format. We infer continuous ground motion along the transect through a projection and interpolation mechanism based on data from stations within 100 km of the transect. In the movies we identify the arrival of surface waves that have high amplitudes. However, over time, although typical Rayleigh type ground motion can be observed, the motion at any given point becomes complex owing to interference of different wave types and different seismic properties of the subsurface. This clearly is different from simple representations of seismic wave propagation in most introductory textbooks. Further, we find a noisy station that shows unusually high amplitude. We refrain from deleting this station in order to demonstrate that in a real world experiment, generally, there will be complexities arising from unexpected behavior of instruments and/or the system under investigation. Explaining such behavior and exploring ways to minimize biases arising from it is an important lesson to learn in introductory science classes. This program can generate visualizations of ground motion from events in the Gulf of California in near real time and with little further development, from events elsewhere.

Joint inversion of seismic and gravity data for imaging seismic velocity structure of the crust and upper mantle beneath Utah, United States

DOE PAGES

Syracuse, Ellen Marie; Zhang, Haijiang; Maceira, Monica

2017-07-11

Here, we present a method for using any combination of body wave arrival time measurements, surface wave dispersion observations, and gravity data to simultaneously invert for three-dimensional P- and S-wave velocity models. The simultaneous use of disparate data types takes advantage of the differing sensitivities of each data type, resulting in a comprehensive and higher resolution three-dimensional geophysical model. In a case study for Utah, we combine body waves first arrivals mainly from the USArray Transportable Array, Rayleigh wave group and phase velocity dispersion data, and Bouguer gravity anomalies to invert for crustal and upper mantle structure of the region.more » Results show clear delineations, visible in both P- and S-wave velocities, between the three main tectonic provinces in the region. In conclusion, without the inclusion of the surface wave and gravity constraints, these delineations are less clear, particularly for S-wave velocities. Indeed, checkerboard tests confirm that the inclusion of the additional datasets dramatically improves S-wave velocity recovery, with more subtle improvements to P-wave velocity recovery, demonstrating the strength of the method in successfully recovering seismic velocity structure from multiple types of constraints.« less

Joint inversion of seismic and gravity data for imaging seismic velocity structure of the crust and upper mantle beneath Utah, United States

DOE Office of Scientific and Technical Information (OSTI.GOV)

Syracuse, Ellen Marie; Zhang, Haijiang; Maceira, Monica

Here, we present a method for using any combination of body wave arrival time measurements, surface wave dispersion observations, and gravity data to simultaneously invert for three-dimensional P- and S-wave velocity models. The simultaneous use of disparate data types takes advantage of the differing sensitivities of each data type, resulting in a comprehensive and higher resolution three-dimensional geophysical model. In a case study for Utah, we combine body waves first arrivals mainly from the USArray Transportable Array, Rayleigh wave group and phase velocity dispersion data, and Bouguer gravity anomalies to invert for crustal and upper mantle structure of the region.more » Results show clear delineations, visible in both P- and S-wave velocities, between the three main tectonic provinces in the region. In conclusion, without the inclusion of the surface wave and gravity constraints, these delineations are less clear, particularly for S-wave velocities. Indeed, checkerboard tests confirm that the inclusion of the additional datasets dramatically improves S-wave velocity recovery, with more subtle improvements to P-wave velocity recovery, demonstrating the strength of the method in successfully recovering seismic velocity structure from multiple types of constraints.« less

Automated seismic detection of landslides at regional scales: a Random Forest based detection algorithm for Alaska and the Himalaya.

NASA Astrophysics Data System (ADS)

Hibert, Clement; Malet, Jean-Philippe; Provost, Floriane; Michéa, David; Geertsema, Marten

2017-04-01

Detection of landslide occurrences and measurement of their dynamics properties during run-out is a high research priority but a logistical and technical challenge. Seismology has started to help in several important ways. Taking advantage of the densification of global, regional and local networks of broadband seismic stations, recent advances now permit the seismic detection and location of landslides in near-real-time. This seismic detection could potentially greatly increase the spatio-temporal resolution at which we study landslides triggering, which is critical to better understand the influence of external forcings such as rainfalls and earthquakes. However, detecting automatically seismic signals generated by landslides still represents a challenge, especially for events with volumes below one millions of cubic meters. The low signal-to-noise ratio classically observed for landslide-generated seismic signals and the difficulty to discriminate these signals from those generated by regional earthquakes or anthropogenic and natural noises are some of the obstacles that have to be circumvented. We present a new method for automatically constructing instrumental landslide catalogues from continuous seismic data. We developed a robust and versatile solution, which can be implemented in any context where a seismic detection of landslides or other mass movements is relevant. The method is based on a spectral detection of the seismic signals and the identification of the sources with a Random Forest algorithm. The spectral detection allows detecting signals with low signal-to-noise ratio, while the Random Forest algorithm achieve a high rate of positive identification of the seismic signals generated by landslides and other seismic sources. We present here the preliminary results of the application of this processing chain in two contexts: i) In Himalaya with the data acquired between 2002 and 2005 by the Hi-Climb network; ii) In Alaska using data recorded by the permanent regional network and the USArray, which is currently being deployed in this region. The landslide seismic catalogues are compared to geomorphological catalogues in terms of number of events and dates when possible.

Persistent Seismicity and Energetics of the 2010 Earthquake Sequence of the Gros Ventre-Teton Area, Wyoming

NASA Astrophysics Data System (ADS)

Farrell, J.

2010-12-01

Farrell, Jamie M. Smith, Robert Massin, Fred White, Bonnie Department of Geology and Geophysics University of Utah Salt Lake City, Utah 84112 Seismicity has persisted along a zone south of the Yellowstone volcanic field in the Gros Ventre Range, Wyoming, and on the eastern edge of the asesimic Quat. high slip-rate Teton fault. Concentrated seismicity has in this area occurs in sporadic sequences documented since 1923 with notable earthquakes in the decade preceding the deadly 1925 Gros Ventre slide that eventually lead to the failure of a dam blocked by the slide in 1927. Notable seismicity of the Gros Ventre region, using data from the Teton, Yellowstone and USArray seismic networks, has continued in the last decade with sequences in 2002, 2004, culminating in an energetic sequence beginning in May, 2009 through a sequence of more than 180 well located earthquakes mainly from August 5 to August 17 of 0.5

Pre-processing ambient noise cross-correlations with equalizing the covariance matrix eigenspectrum

NASA Astrophysics Data System (ADS)

Seydoux, Léonard; de Rosny, Julien; Shapiro, Nikolai M.

2017-09-01

Passive imaging techniques from ambient seismic noise requires a nearly isotropic distribution of the noise sources in order to ensure reliable traveltime measurements between seismic stations. However, real ambient seismic noise often partially fulfils this condition. It is generated in preferential areas (in deep ocean or near continental shores), and some highly coherent pulse-like signals may be present in the data such as those generated by earthquakes. Several pre-processing techniques have been developed in order to attenuate the directional and deterministic behaviour of this real ambient noise. Most of them are applied to individual seismograms before cross-correlation computation. The most widely used techniques are the spectral whitening and temporal smoothing of the individual seismic traces. We here propose an additional pre-processing to be used together with the classical ones, which is based on the spatial analysis of the seismic wavefield. We compute the cross-spectra between all available stations pairs in spectral domain, leading to the data covariance matrix. We apply a one-bit normalization to the covariance matrix eigenspectrum before extracting the cross-correlations in the time domain. The efficiency of the method is shown with several numerical tests. We apply the method to the data collected by the USArray, when the M8.8 Maule earthquake occurred on 2010 February 27. The method shows a clear improvement compared with the classical equalization to attenuate the highly energetic and coherent waves incoming from the earthquake, and allows to perform reliable traveltime measurement even in the presence of the earthquake.

Excitation of seismic waves by a tornado

NASA Astrophysics Data System (ADS)

Valovcin, A.; Tanimoto, T.; Twardzik, C.

2016-12-01

Tornadoes are among the most common natural disasters to occur in the United States. Various methods are currently used in tornado forecasting, including surface weather stations, weather balloons and satellite and Doppler radar. These methods work for detecting possible locations of tornadoes and funnel clouds, but knowing when a tornado has touched down still strongly relies on reports from spotters. Studying tornadoes seismically offers an opportunity to know when a tornado has touched down without requiring an eyewitness report. With the installation of Earthscope's Transportable Array (TA), there have been an increased number of tornadoes that have come within close range of seismometers. We have identified seismic signals corresponding to three tornadoes that occurred in 2011 in the central US. These signals were recorded by the TA station closest to each of the tornado tracks. For each tornado, the amplitudes of the seismic signals increase when the storm is in contact with the ground, and continue until the tornado lifts off some time later. This occurs at both high and low frequencies. In this study we will model the seismic signal generated by a tornado at low frequencies (below 0.1 Hz). We will begin by modeling the signal from the Joplin tornado, an EF5 rated tornado which occurred in Missouri on May 22, 2011. By approximating the tornado as a vertical force, we model the generated signal as the tornado moves along its track and changes in strength. By modeling the seismic waveform generated by a tornado, we can better understand the seismic-excitation process. It could also provide a way to quantitatively compare tornadoes. Additional tornadoes to model include the Calumet-El Reno-Piedmont-Guthrie (CEPG) and Chickasa-Blanchard-Newcastle (CBN) tornadoes, both of which occurred on May 24, 2011 in Oklahoma.

Contrasts in Lower Crustal Structure and Evolution Between the Northern and Southern Rocky Mountains From Xenoliths and Seismic Data

NASA Astrophysics Data System (ADS)

Schulte-Pelkum, V.; Mahan, K. H.; Shen, W.; Stachnik, J. C.

2016-12-01

We compare and contrast crustal structure and composition along a transect from the Southern to Northern Rocky Mountains, with a focus on the lower crust. Evolution of the crust can include processes of emplacement, differentiation, and thermal changes that may generate lower crust with high seismic wavespeeds. The high seismic velocities can be due to mafic composition, the presence of garnet, or both. We seek to find seismic signatures preserved from such processes and compare xenolith samples and present-day seismic appearance between regions with varying tectonic histories. We review recent seismic results from the EarthScope Transportable Array from receiver functions and surface waves, compilations of active source studies, and xenolith studies to compare lower crustal structure along transects through the Northern and Southern Rocky Mountains traversing Montana, Wyoming, Colorado, Utah, and New Mexico. Xenoliths from an unusually thick lower crustal layer with high seismic velocities in Montana record magmatic emplacement processes dating back to the Archean. The lower crustal layer possesses internal velocity contrasts that lead to conflicting interpretations of Moho depth depending on the method used, with xenoliths and a refraction study placing the Moho at 55 km depth, while studies using surface waves and receiver functions identify the largest contrast at 40-45 km depth as the Moho. An additional confounding factor is the presence of metasomatized uppermost mantle with low seismic velocities, which may further diminish the seismic signature of the petrological Moho. To the south, the high-velocity layer diminishes, and seismic velocities in the deep crust under southern Wyoming, Colorado, and New Mexico are lower. In the literature, north-south gradients in lower crustal velocity in this area and observed differences in garnet content have variously been ascribed to thermal dehydration of Archean-age hydrous crust or Laramide-age hydration of previously garnet-rich crust.

Electrical structure of the central Cascadia subduction zone: The EMSLAB Lincoln Line revisited

NASA Astrophysics Data System (ADS)

Evans, Rob L.; Wannamaker, Philip E.; McGary, R. Shane; Elsenbeck, Jimmy

2014-09-01

The EMSLAB experiment was an ambitious onshore-offshore magnetotelluric (MT) transect of the Cascadia subduction zone. When completed (1985-1988), it was the largest experiment of its kind. Modeling and inversion capabilities at the time were, however, not sufficiently sophisticated to handle a fully regularized inversion of the data, including the seafloor data and bathymetric constraints, with the main final model presented based on trial and error forward modeling of the responses. Moreover, new data collected as part of the Earthscope USArray program are of higher quality due to improvements in instrument technology, and augment the original EMSLAB data set, presenting an opportunity to revisit the structure in this part of the subduction system. We have integrated the original wide-band MT data as well as several long-period stations from the original EMSLAB data set and invert these in conjunction with EMSLAB seafloor responses and new Earthscope data on land. This new composite data set has been analyzed in several ways, within a two-dimensional geometry in which conductivity is assumed to be invariant along a strike direction roughly coincident with that of the subduction zone. We have solved for fully smooth regularized models, as well as solutions that allow discontinuities in conductivity along the top surface of the descending slab. Finally, we have tested specific features in the EMSLAB model, notably a moderately shallow ( 30 km depth) forearc conductor. A feature similar to this shallow conductor is a consistent and required feature in our new inversion models, but the new models highlight the connection between the slab and what is interpreted to be an accumulation of aqueous fluids in the deep crust. The depth ( 40 km) at which the conductor intersects the slab suggests that the fluids are released by the transition of hydrous basalt to eclogite at upper greenschist facies and higher metamorphic grade. The nose of the mantle wedge has a conductivity consistent with a dry peridotite composition and thermal models of the system. At a depth of around 80 km the mantle intersecting the slab shows a slight increase in conductivity. This increase is not sufficient to require the presence of melt, but a conductor indicative of melt can be inserted into the model at this depth without compromising the fit.

Roughness of the Mantle Transition Zone Discontinuities Revealed by High Resolution Wavefield Imaging with the Earthscope Transportable Array

NASA Astrophysics Data System (ADS)

Wang, Y.; Pavlis, G. L.

2015-12-01

We post-processed 141,080 pairs of high quality radial and transverse receiver functions from the Earthscope Automated Receiver Survey using a variant of what we have called generalized iterative deconvolution method and reshaped the spiking output into different scales of Ricker wavelets. We then used these data as input to our 3D plane wave migration method to produce an image volume of P to S scattering surfaces under all of the lower 48 states. The result is arguably the highest resolution image ever produce of the mantle transition zone. Due to the effect of migration impulse response, different scales of Ricker wavelets provide another important means of controlling the resolution of the image produced by 3D plane wave migration method. Model simulation shows that comparing to the widely used CCP stacking method with receiver functions shaped by Gaussian wavelet, the application of our methods is capable of resolving not only dipping discontinuities but also more subtle details of the discontinuities. Application to the latest USArray data reveals several previously unobserved features of the 410 and 660 discontinuities. Both discontinuities are resolved to a precision approaching 1 km under the stable interior, but degrading to the order of 10 km in the western US due to a probably combination of higher attenuation and velocity heterogeneity not resolved by current generation tomography models. Topography with many 10s of km is resolved at a range of scales. In addition, we observe large variation of relative amplitude on the radial component and large variations in the radial to transverse amplitude ratio that correlate with inferred variations in discontinuity topography. We argue this combination of observations can be explained by roughness at a range of scales. Roughness is consistent with the phase-change model for these discontinuities given there is little reason to think the mantle is homogeneous at these distance scales. Continental scale isopach of the transition zones shows the average thickness of the transition is approximately 15 km greater in the eastern US compared to the western US. This change occurs on a well define boundary roughly under the Mississippi River. The standard phase change model would thus predict higher transition zone temperatures on the western side of this boundary.

Relationships between Induced Seismicity and Fluid Injection: Development of Strategies to Manage Injection

NASA Astrophysics Data System (ADS)

Eichhubl, Peter; Frohlich, Cliff; Gale, Julia; Olson, Jon; Fan, Zhiqiang; Gono, Valerie

2014-05-01

Induced seismicity during or following the subsurface injection of waste fluids such as well stimulation flow back and production fluids has recently received heightened public and industry attention. It is understood that induced seismicity occurs by reactivation of existing faults that are generally present in the injection intervals. We seek to address the question why fluid injection triggers earthquakes in some areas and not in others, with the aim toward improved injection methods that optimize injection volume and cost while avoiding induced seismicity. A GIS database has been built of natural and induced earthquakes in four hydrocarbon-producing basins: the Fort Worth Basin, South Texas, East Texas/Louisiana, and the Williston Basin. These areas are associated with disposal from the Barnett, Eagle Ford, Bakken, and Haynesville Shales respectively. In each region we analyzed data that were been collected using temporary seismographs of the National Science Foundation's USArray Transportable Array. Injection well locations, formations, histories, and volumes are also mapped using public and licensed datasets. Faults are mapped at a range of scales for selected areas that show different levels of seismic activity, and scaling relationships used to extrapolate between the seismic and wellbore scale. Reactivation potential of these faults is assessed using fault occurrence, and in-situ stress conditions, identifying areas of high and low fault reactivation potential. A correlation analysis between fault reactivation potential, induced seismicity, and fluid injection will use spatial statistics to quantify the probability of seismic fault reactivation for a given injection pressure in the studied reservoirs. The limiting conditions inducing fault reactivation will be compared to actual injection parameters (volume, rate, injection duration and frequency) where available. The objective of this project is a statistical reservoir- to basin-scale assessment of fault reactivation and seismicity induced by fluid injection. By assessing the occurrence of earthquakes (M>2) evenly across large geographic regions, this project differs from previous studies of injection-induced seismicity that focused on earthquakes large enough to cause public concern in well-populated areas. The understanding of triggered seismicity gained through this project is expected to allow for improved design strategies for waste fluid injection to industry and public decision makers.

Geoelectric hazard assessment: the differences of geoelectric responses during magnetic storms within common physiographic zones

NASA Astrophysics Data System (ADS)

Cuttler, Stephen W.; Love, Jeffrey J.; Swidinsky, Andrei

2018-03-01

Geomagnetic field data obtained through the INTERMAGNET program are convolved with with magnetotelluric surface impedance from four EarthScope USArray sites to estimate the geoelectric variations throughout the duration of a magnetic storm. A duration of time from June 22, 2016, to June 25, 2016, is considered which encompasses a magnetic storm of moderate size recorded at the Brandon, Manitoba and Fredericksburg, Virginia magnetic observatories over 3 days. Two impedance sites were chosen in each case which represent different responses while being within close geographic proximity and within the same physiographic zone. This study produces estimated time series of the geoelectric field throughout the duration of a magnetic storm, providing an understanding of how the geoelectric field differs across small geographic distances within the same physiographic zone. This study shows that the geoelectric response of two sites within 200 km of one another can differ by up to two orders of magnitude (4484 mV/km at one site and 41 mV/km at another site 125 km away). This study demonstrates that the application of uniform 1-dimensional conductivity models of the subsurface to wide geographic regions is insufficient to predict the geoelectric hazard at a given site. This necessitates that an evaluation of the 3-dimensional conductivity distribution at a given location is necessary to produce a reliable estimation of how the geoelectric field evolves over the course of a magnetic storm.

Geoelectric hazard assessment: the differences of geoelectric responses during magnetic storms within common physiographic zones

USGS Publications Warehouse

Cuttler, Stephen W.; Love, Jeffrey J.; Swidinsky, Andrei

2018-01-01

Geomagnetic field data obtained through the INTERMAGNET program are convolved with with magnetotelluric surface impedance from four EarthScope USArray sites to estimate the geoelectric variations throughout the duration of a magnetic storm. A duration of time from June 22, 2016, to June 25, 2016, is considered which encompasses a magnetic storm of moderate size recorded at the Brandon, Manitoba and Fredericksburg, Virginia magnetic observatories over 3 days. Two impedance sites were chosen in each case which represent different responses while being within close geographic proximity and within the same physiographic zone. This study produces estimated time series of the geoelectric field throughout the duration of a magnetic storm, providing an understanding of how the geoelectric field differs across small geographic distances within the same physiographic zone. This study shows that the geoelectric response of two sites within 200 km of one another can differ by up to two orders of magnitude (4484 mV/km at one site and 41 mV/km at another site 125 km away). This study demonstrates that the application of uniform 1-dimensional conductivity models of the subsurface to wide geographic regions is insufficient to predict the geoelectric hazard at a given site. This necessitates that an evaluation of the 3-dimensional conductivity distribution at a given location is necessary to produce a reliable estimation of how the geoelectric field evolves over the course of a magnetic storm.

Focusing the EarthScope for a broader audience: Advancing geoscience education with interactive kiosks

NASA Astrophysics Data System (ADS)

Smith-Konter, B. R.; Solis, T.

2012-12-01

A primary objective of the EarthScope Education and Outreach program is to transform technical science into teachable products for a technologically thriving generation. One of the most challenging milestones of scientific research, however, is often the translation of a technical result into a clear teachable moment that is accessible to a broader audience. As 4D multimedia now dominate most aspects of our social environment, science "teaching" now also requires intervention of visualization technology and animation to portray research results in an inviting and stimulating manner. Following the Incorporated Research Institutions for Seismology (IRIS)'s lead in developing interactive Earth science kiosk multimedia (bundled in a free product called Active Earth), we have made a major effort to construct and install customized EarthScope-themed touch screen kiosks in local communities. These kiosks are helping to educate a broader audience about EarthScope's unique instrumentation and observations using interactive animations, games, and virtual field trips. We are also developing new kiosk content that reflect career stories showcasing the personal journeys of EarthScope scientists. To truly bring the interactive aspect of our EarthScope kiosk media into the classroom, we have collaborated with local teachers to develop a one-page EarthScope TerraMap activity worksheet that guides students through kiosk content. These activities are shaping a new pathway for how teachers teach and students learn about planet Earth and its fantastic EarthScope - one click (and touch) at a time.

Seismic Constraints on the Lithosphere-Asthenosphere Boundary Beneath the Izu-Bonin Area: Implications for the Oceanic Lithospheric Thinning

NASA Astrophysics Data System (ADS)

Cui, Qinghui; Wei, Rongqiang; Zhou, Yuanze; Gao, Yajian; Li, Wenlan

2018-01-01

The lithosphere-asthenosphere boundary (LAB) is the seismic discontinuity with negative velocity contrasts in the upper mantle. Seismic detections on the LAB are of great significance in understanding the plate tectonics, mantle convection and lithospheric evolution. In this paper, we study the LAB in the Izu-Bonin subduction zone using four deep earthquakes recorded by the permanent and temporary seismic networks of the USArray. The LAB is clearly revealed with sP precursors (sdP) through the linear slant stacking. As illustrated by reflected points of the identified sdP phases, the depth of LAB beneath the Izu-Bonin Arc (IBA) is about 65 km with a range of 60-68 km. The identified sdP phases with opposite polarities relative to sP phases have the average relative amplitude of 0.21, which means a 3.7% velocity drop and implies partial melting in the asthenosphere. On the basis of the crustal age data, the lithosphere beneath the IBA is located at the 1100 °C isotherm calculated with the GDH1 model. Compared to tectonically stable areas, such as the West Philippine Basin (WPB) and Parece Vela Basin (PVB) in the Philippine Sea, the lithosphere beneath the Izu-Bonin area shows the obvious lithospheric thinning. According to the geodynamic and petrological studies, the oceanic lithospheric thinning phenomenon can be attributed to the strong erosion of the small-scale convection in the mantle wedge enriched in volatiles and melts.

PBO Nucleus Project Status: Integration of 209 Existing GPS Stations into the Plate Boundary Observatory.

NASA Astrophysics Data System (ADS)

Blume, F.; Prescott, W.; Anderson, G.; Eriksson, S.; Feldl, N.

2006-12-01

Tectonic and earthquake research in the US has experienced a quiet revolution over the last decade precipitated by the recognition that slow-motion faulting events can both trigger and be triggered by regular earthquakes. Transient motion has now been found in essentially all tectonic environments, and the detection and analysis of such events is the first-order science target of the EarthScope Project. Because of this and a host of other fundamental tectonics questions that can be answered only with long-duration geodetic time series, the incipient 1400-station EarthScope Plate Boundary Observatory (PBO) network has been designed to leverage 432 existing continuous GPS stations whose measurements extend back over a decade. The irreplaceable recording history of these stations is accelerating EarthScope scientific return by providing the highest possible resolution. This resolution will be used to detect and understand transients, to determine the three-dimensional velocity field (particularly vertical motion), and to improve measurement precision by understanding the complex noise sources inherent in GPS. The PBO Nucleus project supports the operation, maintenance and hardware upgrades of a subset of the six western U.S. geodetic networks until they are subsumed by PBO. Uninterrupted data flow from these stations will effectively double the time-series length of PBO over the expected life of EarthScope, and has created, for the first time, a single GPS-based geodetic network in the US. The other existing sites remain in operation under support from non-NSF sources (e.g. the USGS), and EarthScope continues to benefit from their continued operation. On the grounds of relevance to EarthScope science goals, geographic distribution and data quality, 209 of the 432 existing stations were selected as the nucleus upon which to build PBO. Conversion of these stations to a PBO-compatible mode of operation was begun under previous funding, and as a result data now flow directly to PBO archives and processing centers while maintenance, operations, and meta-data requirements are continuing to be upgraded to PBO standards. At the end of this project all 209 stations will be fully incorporated into PBO, meeting all standards for new PBO construction including data communications and land use permits. Funds for operation of these stations have been included in planned budgets for PBO after the construction phase ends and PBO begins an operational phase in 2008. To date approximately 150 of the 209 stations have been completely upgraded, and data flow from all stations is incorporated into the PBO data analysis flow. The community has only begun to understand the pervasive effects of transient creep, and its societal consequences remained largely unexplored. For example, one open question is whether slow faulting pervasively moderates earthquake nucleation. The existence of slow earthquakes will impact seismic hazards estimation, since these transients are now known to `absorb' a significant component of total slip in some regions and trigger earthquakes in others. The data from these stations serve a much larger audience than just the few people who work to keep them operating. This project is now collecting the data that will be used by the next generation of solid-earth researchers for at least two decades. Educational modules are being developed by a team of researchers, educators, and curriculum development professionals, and are being disseminated through regional and national workshops. An interactive website provides the newest developments in tectonics research to K-16 classrooms.

BASE Flexible Array Preliminary Lithospheric Structure Analysis

NASA Astrophysics Data System (ADS)

Yeck, W. L.; Sheehan, A. F.; Anderson, M. L.; Siddoway, C. S.; Erslev, E.; Harder, S. H.; Miller, K. C.

2009-12-01

The Bighorns Arch Seismic Experiment (BASE) is a Flexible Array experiment integrated with EarthScope. The goal of BASE is to develop a better understanding of how basement-involved foreland arches form and what their link is to plate tectonic processes. To achieve this goal, the crustal structure under the Bighorn Mountain range, Bighorn Basin, and Powder River Basin of northern Wyoming and southern Montana are investigated through the deployment of 35 broadband seismometers, 200 short period seismometers, 1600 “Texan” instruments using active sources and 800 “Texan” instruments monitoring passive sources, together with field structural analysis of brittle structures. The novel combination of these approaches and anticipated simultaneous data inversion will give a detailed structural crustal image of the Bighorn region at all levels of the crust. Four models have been proposed for the formation of the Bighorn foreland arch: subhorizontal detachment within the crust, lithospheric buckling, pure shear lithospheric thickening, and fault blocks defined by lithosphere-penetrating thrust faults. During the summer of 2009, we deployed 35 broadband instruments, which have already recorded several magnitude 7+ teleseismic events. Through P wave receiver function analysis of these 35 stations folded in with many EarthScope Transportable Array stations in the region, we present a preliminary map of the Mohorovicic discontinuity. This crustal map is our first test of how the unique Moho geometries predicted by the four hypothesized models of basement involved arches fit seismic observations for the Bighorn Mountains. In addition, shear-wave splitting analysis for our first few recorded teleseisms helps us determine if strong lithospheric deformation is preserved under the range. These analyses help lead us to our final goal, a complete 4D (3D spatial plus temporal) lithospheric-scale model of arch formation which will advance our understanding of the mechanisms accommodating and driving basement-involved arch formation as well as continental lithospheric rheology.

Love-to-Rayleigh Conversions and Seismic Anisotropy in Cascadia

NASA Astrophysics Data System (ADS)

Rieger, Duayne Matthew

Seismic anisotropy is often attributed to the development of lattice-preferred orientation (LPO) of olivine crystals in peridotite, induced by the dislocation creep component of mantle deformation (Karato et al., 2008; Ribe, 1992). Mantle-flow-induced seismic anisotropy is often modeled in the simple form of hexagonal symmetry, where the anisotropic volume is uniaxially fast or slow. This relationship between seismic anisotropy and mantle deformation allows for the mapping of mantle dynamics using measurements of seismic anisotropy. Presently, methods of measuring seismic anisotropy in Earth's mantle include shear-wave splitting and surface-wave tomography. These methods are tuned to seismically fast axes laying in the horizontal or surface-tangent plane and are limited in discerning clipping seismic fast axes. This is a shortcoming. It is reasonable to suspect the presence of dipping seismic fast axes induced by mantle flow in several tectonic regimes such as subduction zones. The slab rollback model of the subduction zone system has been argued to exhibit trench-parallel subslab anisotropy due to the lateral evacuation of the subslab mantle material (Hall et al., 2000; Russo and Silver, 1994). This model has been emboldened by the dominance of trench-parallel shear-wave-splitting measurements in the subslab mantle of global subduction zones. This model has significant geodynamic implications, requiring viscous decoupling between the subslab mantle and the sub-ducting slab. The Cascadian subduction zone is of particular scientific interest. While experiencing slab rollback (Zandt and Humphreys, 2008), trench-perpendicular shear-wave-splitting measurements are observed in the subslab mantle of Cascadia (Currie et al., 2004; Eakin et al., 2010; Long and Silver, 2008; 2009). This suggests either viscous coupling resulting in slab-entrained flow or the presence of an alternate relationship between finite strain in the mantle and seismic anisotropy. The ability to discern a clipping anisotropic axis would help gain insight into the mantle dynamics of regions such as Cascadia. Lateral gradients of seismic anisotropy in Earth's upper mantle induce coupling among Earth's spheroidal and toroidal normal modes. This coupling can manifest as observable surface-wave polarization anomalies resulting from Love to Rayleigh wave conversions. These Love to Rayleigh conversions are known in the literature as Quasi-Love (QL) waves (Park and Yu, 1992) and are sensitive to both the strike and the dip of an anisotropic symmetry axis. In this dissertation I investigate the phenomenology of QL surface-wave scattering, including its sensitivity to the type and orientation of seismic anisotropy. I then apply my findings to observations of QL wave scattering in Cascada in order to further constrain subslab mantle anisotropy in the region. First, I make initial observations and confirm the presence of QL scattering in Cascada and the western U.S. using data recorded on USArray. I then move on to develop an algorithm to model efficiently QL wave scattering in the presence of 3-dimensional anisotropic structure. Using this forward-modeling algorithm, I investigate the dependence of QL wave scattering on the type and orientation of seismic Anisotropy. I find that P and S anisotropies exhibit independent effects on scattering. Scattering due to S anisotropy is stronger than that due to P anisotropy for all orientations and dominates in the observed scattering pattern. Both the phase and amplitude of the QL wave is dependent on the orientation (strike and dip) of the symmetry axis relative to the incident propagation azimuth of the source-receiver great-circle path. Due to this, the orientation of the anisotropic symmetry axis provides a distinct signature which is observable in the variation of QL wave scattering with wave-propagation azimuth. Finally, using data recorded on USArray, I observe the variation in QL wave scattering with propagation azimuth. I then attempt to forward-model the observed behavior using the algorithm developed earlier. The best-fitting model suggests coherent trench-perpendicular mantle anisotropy with an eastward dip in the sublsab mantle of the Cascadian subduction zone. The resulting anisotropic model adds confidence to the entrained subslab mantle-flow model for Cascadia and further refutes the 3-D return-flow model associated with slab rollback.

SeismoDome: Sonic and visual representation of earthquakes and seismic waves in the planetarium

NASA Astrophysics Data System (ADS)

Holtzman, B. K.; Candler, J.; Repetto, D.; Pratt, M. J.; Paté, A.; Turk, M.; Gualtieri, L.; Peter, D. B.; Trakinski, V.; Ebel, D. S. S.; Gossmann, J.; Lem, N.

2017-12-01

Since 2014, we have produced four "Seismodome" public programs in the Hayden Planetarium at the American Museum of Natural History in New York City. To teach the general public about the dynamics of the Earth, we use a range of seismic data (seismicity catalogs, surface and body wave fields, ambient noise, free oscillations) to generate movies and sounds conveying aspects of the physics of earthquakes and seismic waves. The narrative aims to stretch people's sense of time and scale, starting with 2 billion years of convection, then zooming in seismicity over days to twenty years at different length scales, to hours of global seismic wave propagation, all compressed to minute long movies. To optimize the experience in the planetarium, the 180-degree fisheye screen corresponds directly to the surface of the Earth, such that the audience is inside the planet. The program consists of three main elements (1) Using sonified and animated seismicity catalogs, comparison of several years of earthquakes on different plate boundaries conveys the dramatic differences in their dynamics and the nature of great and "normal" earthquakes. (2) Animations of USArray data (based on "Ground Motion Visualizations" methods from IRIS but in 3D, with added sound) convey the basic observations of seismic wave fields, with which we raise questions about what they tell us about earthquake physics and the Earth's interior structure. (3) Movies of spectral element simulations of global seismic wave fields synchronized with sonified natural data push these questions further, especially when viewed from the interior of the planet. Other elements include (4) sounds of the global ambient noise field coupled to movies of mean ocean wave height (related to the noise source) and (5) three months of free oscillations / normal modes ringing after the Tohoku earthquake. We use and develop a wide range of sonification and animation methods, written mostly in python. Flat-screen versions of these movies are available on the Seismic Sound Lab (LDEO) website. Here, we will present a subset of the methods an overview of the aims of the program.

ENAM: A community seismic experiment targeting rifting processes and post-rift evolution of the Mid Atlantic US margin

NASA Astrophysics Data System (ADS)

Van Avendonk, H. J.; Magnani, M. B.; Shillington, D. J.; Gaherty, J. B.; Hornbach, M. J.; Dugan, B.; Long, M. D.; Lizarralde, D.; Becel, A.; Benoit, M. H.; Harder, S. H.; Wagner, L. S.; Christeson, G. L.

2014-12-01

The continental margins of the eastern United States formed in the Early Jurassic after the breakup of supercontinent Pangea. The relationship between the timing of this rift episode and the occurrence of offshore magmatism, which is expressed in the East Coast Magnetic Anomaly, is still unknown. The possible influence of magmatism and existing lithospheric structure on the rifting processes along margin of the eastern U.S. was one of the motivations to conduct a large-scale community seismic experiment in the Eastern North America (ENAM) GeoPRISMS focus site. In addition, there is also a clear need for better high-resolution seismic data with shallow penetration on this margin to better understand the geological setting of submarine landslides. The ENAM community seismic experiment is a project in which a team of scientists will gather both active-source and earthquake seismic data in the vicinity of Cape Hatteras on a 500 km wide section of the margin offshore North Carolina and Virginia. The timing of data acquisition in 2014 and 2015 facilitates leveraging of other geophysical data acquisition programs such as Earthscope's Transportable Array and the USGS marine seismic investigation of the continental shelf. In April of 2014, 30 broadband ocean-bottom seismometers were deployed on the shelf, slope and abyssal plain of the study site. These instruments will record earthquakes for one year, which will help future seismic imaging of the deeper lithosphere beneath the margin. In September and October of 2014, regional marine seismic reflection and refraction data will be gathered with the seismic vessel R/V Marcus Langseth, and airgun shots will also be recorded on land to provide data coverage across the shoreline. Last, in the summer of 2015, a land explosion seismic refraction study will provide constraints on the crustal structure in the adjacent coastal plain of North Carolina and Virginia. All seismic data will be distributed to the community through IRIS/DMC and the LDEO/UTIG Seismic data center. Two workshops are planned for 2015, where new users get an opportunity to engage in basic processing and analysis of the new data set.

Plate Boundary Observatory Strainmeter Recordings of The M6.0 August 24, 2014 South Napa Earthquake

NASA Astrophysics Data System (ADS)

Hodgkinson, Kathleen; Mencin, David; Phillips, David; Mattioli, Glen; Meertens, Charles

2015-04-01

The 2014 Mw6.0 South Napa earthquake nucleated at 11 km depth near the West Napa fault, one of a complex system of sub-parallel major right lateral faults north of San Francisco that together accommodate much of the relative motion between the Pacific and North American tectonic plates. The South Napa event was the largest to have shaken the San Francisco Bay Area (SFBA) in almost 25 years. A major goal of the NSF-funded EarthScope Plate Boundary Observatory (PBO), installed and maintained by UNAVCO, was to enable researchers to study the interaction between the faults that form a plate boundary zone, and in particular, to investigate the role that aseismic transients contribute to strain accumulation and release. To realize this goal, PBO includes borehole tensor strainmeters (BSMs) installed in several targeted regions, including on to the north and east of San Francisco. Two PBO BSMs have been operating in the SFBA since 2008: B057, north of San Francisco and 30 km from the epicenter, and B054, 3 km from the Hayward Fault and 40 km from the epicenter. We find the coseismic strains recorded by B057 are close to those predicted using elastic half-space dislocation theory and the seismically determined focal mechanism, while a more complicated variable slip model may be required for observations from B054. Months after the event, B057 continued to record a significant postseismic signal. In this presentation we document the coseismic signals recorded by the PBO BSMs and characterize the temporal behavior of the postseismic signal at B057. The PBO network includes over 1100 GPS, 75 BSMs, 79 seismometers and arrays of tiltmeters, pore pressure sensors and meteorological instrumentation. UNAVCO generates an Earthscope Level 2 processed strain time-series combined into areal and shear strains for the PBO BSM network; the raw data are available from the IRIS DMC in mSEED format. For events of interest, such as the South Napa earthquake, UNAVCO generates a 1-sps processed strain time series that also includes tilt data, pore pressure and high-rate meteorological measurements if available. Site information, data quality measurements, current strain plots and strain time-series for all PBO strain instruments can be obtained from the UNAVCO PBO web page (http://www.unavco.org/data/strain-seismic/strain-seismic.html).

Seismicity in Oklahoma Before Prague

NASA Astrophysics Data System (ADS)

Delorey, A. A.; Johnson, P. A.

2017-12-01

The 2011 M5.7 Prague earthquake was the first large anthropogenically induced earthquake in Oklahoma. Since then, three more M5+ earthquakes followed it near Fairview, Pawnee, and Cushing. Oklahoma induced seismicity has garnered a lot of attention from both the media and the scientific community. But, little is known about seismicity in Oklahoma prior to the Prague earthquake due to a lack of instrumentation. We ask the question, "Was there any indication in the geophysical record prior to the Prague earthquake that bigger earthquakes were becoming more likely?" Fortunately, stations from Earthscope's Transportable Array were in Oklahoma during 2010 and 2011 providing a sparse, but still useful data set. Using our microseismicity detector called Interstation Seismic Coherence, we were able to catalog over 3000 earthquakes with a magnitude of completeness around 2.0 in northeastern Oklahoma over 17 months between June 2010 and the Prague earthquake in November 2011. During this period of time there are less than 200 earthquakes in the ANSS Comprehensive Catalog and 900 in the catalog produced by the Array Network Facility at the UCSD using Transportable Array stations. The M>5 earthquakes occurred in a region where stress conditions and seismicity rates were evolving much faster than they do in many natural systems presenting an opportunity to study the time dependence of upper crustal behavior. A clustering analysis shows that earthquakes occurring in northeastern Oklahoma during 2010-2011 are highly correlated with the magnitude of solid earth tides. Although some aftershocks and clusters were recorded following the Prague earthquake using temporary arrays, regional seismicity is not well recorded again until later in 2013. Of note, after 2013, we no longer observe tidal correlation suggesting the ensemble of fault criticality has evolved. One explanation for this change in earthquake behavior is a change in poroelastic conditions.

Site Assessment of a New State-Wide Seismic Network in Texas (TexNet)

NASA Astrophysics Data System (ADS)

Savvaidis, A.; Young, B.; Mukherjee, T.; Hennings, P.; Rathje, E.; Zalachoris, G.; Young, M.; Walter, J. I.; DeShon, H. R.; Frohlich, C.

2016-12-01

Earthquake activity has recently increased in the southern mid-continent of the U.S., including Texas. To monitor seismicity activity in the state of Texas, a new seismicity monitoring program known as TexNet, was funded by the Texas State Legislature in 2015. TexNet consists of 22 new permanent broadband (120s post-hole) seismic stations that will complement the 17 stations currently operating in the State. These permanent stations will provide the baseline seismicity of the state. In addition, 36 portable stations (incorporating both a 20s post-hole seismometer and a post-hole accelerometer) will be used to densify the network in specific areas, of the State, depending on measured seismicity level, proximity to infrastructure, or other scientific investigations. One goal for TexNet is to provide authenticated data needed to evaluate the location, and frequency of earthquakes. To minimize the uncertainties in earthquake locations and increase detectability of the network, an extensive site assessment survey was conducted. The initial station positions were chosen based on Earthscope, Transportable Array (TA) site positions, while ensuring that the stations were relatively evenly-spaced across the State. We then analyzed the noise and earthquake data from the TA seismometers, and added new locations based on geology, topography, and absence of nearby human activities. A 30-min noise test was conducted at each site to identify the site amplification using HVSR information. A 24-hr survey then followed, where the noise level during day and night was identified, analyzed using power spectral density and compared to the NHNM and NLNM (Peterson, 1993; USGS Open File Report, 322). Based on these survey results nearby alternative sites were evaluated to improve final site position. Full deployment and data streaming is expected by December 2016, and will be discussed during this presentation.

Site Assessment of a New State-Wide Seismic Network in Texas (TexNet), USA.

NASA Astrophysics Data System (ADS)

Savvaidis, Alexandros; Young, Bissett; Hennings, Peter; Rathje, Ellen; Zalachoris, George; Young, Michael H.; Walter, Jacob I.; DeShon, Heather R.; Frohlich, Cliff

2017-04-01

Earthquake activity has recently increased in the southern mid-continent of the U.S., including Texas. To monitor seismicity activity in the state of Texas, a new seismicity monitoring program known as TexNet, was funded by the Texas State Legislature in 2015. TexNet consists of 22 new permanent broadband (120s post-hole) seismic stations that will complement the 17 stations currently operating in the State. These permanent stations will provide the baseline seismicity of the state. In addition, 36 portable stations (incorporating both a 20s post-hole seismometer and a post-hole accelerometer) will be used to densify the network in specific areas, of the State, depending on measured seismicity level, proximity to infrastructure, or other scientific investigations. One goal for TexNet is to provide authenticated data needed to evaluate the location, and frequency of earthquakes. To minimize the uncertainties in earthquake locations and increase detectability of the network, an extensive site assessment survey was conducted. The initial station positions were chosen based on Earthscope, Transportable Array (TA) site positions, while ensuring that the stations were relatively evenly-spaced across the State. We then analyzed the noise and earthquake data from the TA seismometers, and added new locations based on geology, topography, and absence of nearby human activities. A 30-min noise test was conducted at each site to identify the site amplification using HVSR information. A 24-hr survey then followed, where the noise level during day and night was identified, analyzed using power spectral density and compared to the NHNM and NLNM (Peterson, 1993; USGS Open File Report, 322). Based on these survey results nearby alternative sites were evaluated to improve final site position. Deployment and data streaming started on September 2016, and will be discussed during this presentation.

Upper mantle anisotropic attenuation of the Sierra Nevada and surroundings

NASA Astrophysics Data System (ADS)

Bernardino, M. J.; Jones, C. H.; Monsalve, G.

2016-12-01

We investigate the contribution of anelasticity in the generation of seismic velocity variations within the upper mantle of the Sierra Nevada and surrounding regions through teleseismic shear-wave attenuation. Given that anelastic effects are most sensitive to temperature and hydration and less to composition and small degrees of partial melt, we aim constrain the thermal structure beneath this region and identify locations where elevated upper mantle temperatures dominate. We also investigate the dependence of shear-wave attenuation on direction by accounting for seismic anisotropy in our measurements. S-wave t* values are determined from teleseismic S- and SKS- phases recorded on permanent and temporary deployments within the California region with particular focus on the Sierra Nevada Earthscope Project (SNEP) and the Sierran Paradox Experiment (SPE) stations. S-waveforms are rotated into the Sierran SFast, N75°E, and SSlow, N15°W, components. Following the method of Stachnik et al., (2004), S-wave spectra for each event are jointly inverted for a single seismic moment, M0k, and corner frequency, fck, for each event, and separate t* for each ray path. The resulting t*Fast and t*Slow measurements are then inverted for three-dimensional variations in (1/QFast) and (1/QSlow). Results are compared with previous magnetotelluric, surface heat flow, and body-wave velocity inversion studies.

Core-Mantle Boundary Complexities beneath the Mid-Pacific

NASA Astrophysics Data System (ADS)

Sun, D.; Helmberger, D. V.; Jackson, J. M.

2016-12-01

The detailed core-mantle boundary (CMB) structures beneath the Mid-Pacific are important to map the boundary of Large Low Shear Velocity Province (LLSVP) and the location of ultra-low velocity zone (ULVZ) related to the LLSVP and the D" layer, which are crucial for answering the key questions regarding to the mantle dynamics. Seismic data from deep earthquakes in the Fiji-Tonga region recorded by stations of USArray provide great sampling of the CMB beneath the Mid-Pacific. Here we explore the USArray data with different seismic phases to study the CMB complexities beneath the Mid-Pacific. First, we examined the differential travel time and amplitude between ScS and S for data at western US and confirm the northeastern boundary of the mid-Pacific LLSVP. The delayed ScS-S travel times and smaller amplitude of ScS require the existence of ULVZ locally. Secondly, the Sdiff data recorded by stations at central US shows variation in multi-pathing, that is, the presence of secondary arrivals following the S phase at diffracted distances (Sdiff) which suggests that the waveform complexity is due to structures at the eastern edge of the mid-Pacific LLSVP. This study reinforces previous studies that indicate late arrivals occurring after the primary Sdiff arrivals. A tapered wedge structure with low shear velocity allows for wave energy trapping, producing the observed waveform complexity and delayed arrivals at large distances. The location of the low velocity anomaly agrees with that inferred from the ScS-S measurements. We also observed advanced SV arrivals, which can be explained by the emerging of the D" discontinuity to the east of the boundary of the LLSVP to produce a "pseudo anisotropy". Thirdly, the arrivals of the SPdKS phase support the presence of an ULVZ within a two-humped LLSVP. A sharp 10 secs jump of the differential travel time between S and SKS (TS-SKS) across distance range of 5° is observed. The associated SKS waveform distortions suggest that the differential travel time anomaly is mainly controlled by the SKS, which is explained by a possible slab subducted to the lower mantle.

Innovations in making EarthScope science and data accessible (Invited)

NASA Astrophysics Data System (ADS)

Pratt-Sitaula, B. A.; Butler, R. F.; Whitman, J. M.; Granshaw, F. D.; Lillie, R. J.; Hunter, N.; Cronin, V. S.; Resor, P. G.; Olds, S. E.; Miller, M. S.; Walker, R.; Douglas, B. B.

2013-12-01

EarthScope is a highly complex technical and scientific endeavor. Making results from EarthScope accessible to the general public, educators, all levels of students, and even geoscience professionals from other disciplines is a very real challenge that must be overcome to realize EarthScope's intended broader impacts of contributing 'to the mitigation of risks from geological hazards ... and the public's understanding of the dynamic Earth.' Here we provided several case examples of how EarthScope science can be effectively communicated and then scaled to reach different or larger audiences. One approach features providing professional development regarding EarthScope and geohazard science to non-university educators who then scale up the impact by communicating to hundreds or even thousands of students and general public members each. EarthScope-funded Teachers on the Leading Edge (TOTLE) ran workshops 2008-2010 for 120 Pacific Northwest teachers and community college educators who subsequently communicated EarthScope and geohazards science to >30,000 students and >1500 other adults. Simultaneously EarthScope's National Office at Oregon State University was running workshops for park interpreters who have since reached >>100,000 park visitors. These earlier projects have served as the foundation for the new Cascadia EarthScope Earthquake and Tsunami Education Program (CEETEP), which is currently running joint workshops for coastal Oregon and Washington teachers, interpreters, and emergency management educators. The other approach featured here is UNAVCO's scaled efforts to make Plate Boundary Observatory (PBO) and other geodetic data more accessible to introductory and majors-level geoscience students and faculty. Initial projects included development of a Teaching Geodesy website on the Science Education Research Center (SERC) and development of teaching modules and activities that use PBO data. Infinitesimal strain analysis using GPS data is a 1-2 week module for majors-level structural geology or geophysics courses that is now published on SERC and UNAVCO websites. Simpler exercises using PBO data have been beta-tested for introductory courses as well. Now UNAVCO has received NSF-funding to develop four more modules (two each for introductory and majors-level) that will feature PBO and other geodetic data. The goal is for these four to serve as the foundation for an ultimate collection of >10 modules.

A dipping, thick Farallon slab below central United States

NASA Astrophysics Data System (ADS)

Sun, D.; Gurnis, M.; Saleeby, J.; Helmberger, D. V.

2015-12-01

It has been hypothesized that much of the Laramide orogeny was caused by dynamic effects induced by an extensive flat slab during a period of plateau subduction. A particularly thick block containing the Shatsky Rise conjugate, now in the mid-mantle, left a distinctive deformation footprint from southern California to Denver, Colorado. Thus mid-mantle, relic slabs can provide fundamental information about past subduction and the history of plate tectonics if properly imaged. Here we find clear evidence for a northeastward dipping (35° dip), slab-like, but fat (up to 400-500 km thick) seismic anomaly within the top of the lower mantle below the central United States. Using a deep focus earthquake below Spain with direct seismic paths that propagate along the top and bottom of the anomaly, we find that the observed, stacked seismic waveforms recorded with the dense USArray show multi-pathing indicative of sharp top and bottom surfaces. Plate tectonic reconstructions in which the slab is migrated back in time suggest strong coupling of the slab to North America. In combination with the reconstructions, we interpret the structure as arising from eastward dipping Farallon subduction at the western margin of North America during the Cretaceous, in contrast with recent interpretations. The slab could have been fattened through a combination of pure shear thickening during flat-slab subduction and a folding instability during penetration into the lower mantle.

Double-Difference Global Adjoint Tomography

NASA Astrophysics Data System (ADS)

Orsvuran, R.; Bozdag, E.; Lei, W.; Tromp, J.

2017-12-01

The adjoint method allows us to incorporate full waveform simulations in inverse problems. Misfit functions play an important role in extracting the relevant information from seismic waveforms. In this study, our goal is to apply the Double-Difference (DD) methodology proposed by Yuan et al. (2016) to global adjoint tomography. Dense seismic networks, such as USArray, lead to higher-resolution seismic images underneath continents. However, the imbalanced distribution of stations and sources poses challenges in global ray coverage. We adapt double-difference multitaper measurements to global adjoint tomography. We normalize each DD measurement by its number of pairs, and if a measurement has no pair, as may frequently happen for data recorded at oceanic stations, classical multitaper measurements are used. As a result, the differential measurements and pair-wise weighting strategy help balance uneven global kernel coverage. Our initial experiments with minor- and major-arc surface waves show promising results, revealing more pronounced structure near dense networks while reducing the prominence of paths towards cluster of stations. We have started using this new measurement in global adjoint inversions, addressing azimuthal anisotropy in upper mantle. Meanwhile, we are working on combining the double-difference approach with instantaneous phase measurements to emphasize contributions of scattered waves in global inversions and extending it to body waves. We will present our results and discuss challenges and future directions in the context of global tomographic inversions.

Short-Period Surface Wave Based Seismic Event Relocation

NASA Astrophysics Data System (ADS)

White-Gaynor, A.; Cleveland, M.; Nyblade, A.; Kintner, J. A.; Homman, K.; Ammon, C. J.

2017-12-01

Accurate and precise seismic event locations are essential for a broad range of geophysical investigations. Superior location accuracy generally requires calibration with ground truth information, but superb relative location precision is often achievable independently. In explosion seismology, low-yield explosion monitoring relies on near-source observations, which results in a limited number of observations that challenges our ability to estimate any locations. Incorporating more distant observations means relying on data with lower signal-to-noise ratios. For small, shallow events, the short-period (roughly 1/2 to 8 s period) fundamental-mode and higher-mode Rayleigh waves (including Rg) are often the most stable and visible portion of the waveform at local distances. Cleveland and Ammon [2013] have shown that teleseismic surface waves are valuable observations for constructing precise, relative event relocations. We extend the teleseismic surface wave relocation method, and apply them to near-source distances using Rg observations from the Bighorn Arche Seismic Experiment (BASE) and the Earth Scope USArray Transportable Array (TA) seismic stations. Specifically, we present relocation results using short-period fundamental- and higher-mode Rayleigh waves (Rg) in a double-difference relative event relocation for 45 delay-fired mine blasts and 21 borehole chemical explosions. Our preliminary efforts are to explore the sensitivity of the short-period surface waves to local geologic structure, source depth, explosion magnitude (yield), and explosion characteristics (single-shot vs. distributed source, etc.). Our results show that Rg and the first few higher-mode Rayleigh wave observations can be used to constrain the relative locations of shallow low-yield events.

Anomalous mantle transition zone beneath the Yellowstone hotspot track

NASA Astrophysics Data System (ADS)

Zhou, Ying

2018-06-01

The origin of the Yellowstone and Snake River Plain volcanism has been strongly debated. The mantle plume model successfully explains the age-progressive volcanic track, but a deep plume structure has been absent in seismic imaging. Here I apply diffractional tomography to receiver functions recorded at USArray stations to map high-resolution topography of mantle transition-zone discontinuities. The images reveal a trail of anomalies that closely follow the surface hotspot track and correlate well with a seismic wave-speed gap in the subducting Farallon slab. This observation contradicts the plume model, which requires anomalies in the mid mantle to be confined in a narrow region directly beneath the present-day Yellowstone caldera. I propose an alternative interpretation of the Yellowstone volcanism. About 16 million years ago, a section of young slab that had broken off from a subducted spreading centre in the mantle first penetrated the 660 km discontinuity beneath Oregon and Idaho, and pulled down older stagnant slab. Slab tearing occurred along pre-existing fracture zones and propagated northeastward. This reversed-polarity subduction generated passive upwellings from the lower mantle, which ascended through a water-rich mantle transition zone to produce melting and age-progressive volcanism.

A study of infrasonic anisotropy and multipathing in the atmosphere using seismic networks.

PubMed

Hedlin, Michael A H; Walker, Kristoffer T

2013-02-13

We discuss the use of reverse time migration (RTM) with dense seismic networks for the detection and location of sources of atmospheric infrasound. Seismometers measure the response of the Earth's surface to infrasound through acoustic-to-seismic coupling. RTM has recently been applied to data from the USArray network to create a catalogue of infrasonic sources in the western US. Specifically, several hundred sources were detected in 2007-2008, many of which were not observed by regional infrasonic arrays. The influence of the east-west stratospheric zonal winds is clearly seen in the seismic data with most detections made downwind of the source. We study this large-scale anisotropy of infrasonic propagation, using a winter and summer source in Idaho. The bandpass-filtered (1-5 Hz) seismic waveforms reveal in detail the two-dimensional spread of the infrasonic wavefield across the Earth's surface within approximately 800 km of the source. Using three-dimensional ray tracing, we find that the stratospheric winds above 30 km altitude in the ground-to-space (G2S) atmospheric model explain well the observed anisotropy pattern. We also analyse infrasound from well-constrained explosions in northern Utah with a denser IRIS PASSCAL seismic network. The standard G2S model correctly predicts the anisotropy of the stratospheric duct, but it incorrectly predicts the dimensions of the shadow zones in the downwind direction. We show that the inclusion of finer-scale structure owing to internal gravity waves infills the shadow zones and predicts the observed time durations of the signals. From the success of this method in predicting the observations, we propose that multipathing owing to fine scale, layer-cake structure is the primary mechanism governing propagation for frequencies above approximately 1 Hz and infer that stochastic approaches incorporating internal gravity waves are a useful improvement to the standard G2S model for infrasonic propagation modelling.

The Processes Producing the Actively Uplifting Mackenzie Mountains in the Yukon and Northwest Territories, Canada

NASA Astrophysics Data System (ADS)

Rasmussen, B.; Aster, R. C.; Schutt, D.

2016-12-01

The actively uplifting and seismically active Mackenzie Mountains in the Yukon and Northwest Territories of Canada exist nearly 800 km from the Pacific plate subduction zone. As such, it is clear that traditional subduction zone orogenic mechanics are not at play. This mountain range may present a model for uplift of other ranges distant from plate boundaries, such as the Rockies or Ancestral Rockies. Due to its remote location, this region's lithospheric structure is poorly constrained. However, two hypotheses have been developed recently. The first proposes that stress from the Yakutat Indentor as it subducts under North America at the Gulf of Alaska is transferred deep inland through the upper crust, and that the lower crust and mantle lithosphere are very weak. As this weak lithosphere meets the strong Canadian Craton, lateral translation turns into uplift, forming the Mackenzies (Mazzotti and Hyndman, 2002, Geology, v. 30, no.6). Alternatively, it may be that mantle flow from the north is deflected eastward by the Yakutat slab, producing large scale mantle flow and stress which propagates through the crust to uplift the Mackzenzie Mountains without an abnormally weak lithosphere (Finzel, 2015, Geophys. Res. Lett., 42, 4350-4358). Both cases imply distinct isotropic and anisotropic structure that will be constrained through Rayleigh wave tomography. Notably, we will take advantage of the recent deployment of several Earthscope Transportable Array stations nearby, and some preliminary data from the ongoing Mackenzie Mountains Earthscope Project.

Scars of the Farallon Plate in the High Plains Revealed by 3D Wavefield Imaging with the Earthscope Transportable Array

NASA Astrophysics Data System (ADS)

Pavlis, G. L.; Yang, X.

2012-12-01

We used P to S conversion data from the Earthscope Automated Receiver function Survey (EARS) to image the upper mantle from the west coast to the Mississippi River. We used 178,300 radial and transverse receiver function estimates that survived automated editing procedures defined by EARS. Processing delays by EARS limited the data to the period through April 5, 2012. We processed these data with a three-component, fully three-dimensional, prestack, wavefield imaging procedure that we have referred to previously as plane-wave migration. Previous results with earlier generations of the EARS data and the same technique revealed the presence of a continuous, east-dipping horizon throughout the entire Cordillera between a depth of approximately 200-450 km with hints of penetration of this horizon through the 410 km discontinuity. This surface was interpreted as a marker on the top of the actively subducting Juan de Fuca/Farallon slab through cross-validation with all published body wave tomography models derived from USArray data. The new results reveal a surprisingly similar feature under the high plains. We observe a high-amplitude, east-dipping horizon that begins near the Rocky Mountain front and intersects the 410 km discontinuity at approximately the longitude of the Kansas-Missouri border. The lateral extent of this feature, however, is more limited. It disappears to the north around the Kansas-Nebraska border and to the south within central Texas. This region corresponds closely with the "big break" defined in tomography models of Sigloch (2011. She interpreted this feature as a residual signature of a westward jump of the Farallon slab at the close of the Laramide orogeny that is commonly viewed as a period of flat-slab subduction. We suggest the feature we image is equivalent to the east-dipping feature presently seen under the Cordillera. The feature imaged in the Cordillera can be directly linked to active processes. If a comparable process maintains what we see in the high plains it may mark a boundary where the cratonic keel is overriding the mantle above the transition zone along a zone of deformation originally created in the Laramide. This may be an explanation of the elevated topography of the high plains. An alternative explanation is we are seeing a residual scar from the Laramide, but that would require this region of the mantle to have been static for the order of 70 Myr and that the craton moves over the mantle along a thin deformation zone.

A joint local and teleseismic tomography study of the Mississippi Embayment and New Madrid Seismic Zone

NASA Astrophysics Data System (ADS)

Nyamwandha, Cecilia A.; Powell, Christine A.; Langston, Charles A.

2016-05-01

Detailed, upper mantle P and S wave velocity (Vp and Vs) models are developed for the northern Mississippi Embayment (ME), a major physiographic feature in the Central United States (U.S.) and the location of the active New Madrid Seismic Zone (NMSZ). This study incorporates local earthquake and teleseismic data from the New Madrid Seismic Network, the Earthscope Transportable Array, and the FlexArray Northern Embayment Lithospheric Experiment stations. The Vp and Vs solutions contain anomalies with similar magnitudes and spatial distributions. High velocities are present in the lower crust beneath the NMSZ. A pronounced low-velocity anomaly of ~ -3%--5% is imaged at depths of 100-250 km. High-velocity anomalies of ~ +3%-+4% are observed at depths of 80-160 km and are located along the sides and top of the low-velocity anomaly. The low-velocity anomaly is attributed to the presence of hot fluids upwelling from a flat slab segment stalled in the transition zone below the Central U.S.; the thinned and weakened ME lithosphere, still at slightly higher temperatures from the passage of the Bermuda hotspot in mid-Cretaceous, provides an optimal pathway for the ascent of the fluids. The observed high-velocity anomalies are attributed to the presence of mafic rocks emplaced beneath the ME during initial rifting in the early Paleozoic and to remnants of the depleted, lower portion of the lithosphere.

Seismic Noise Analysis and Reduction through Utilization of Collocated Seismic and Atmospheric Sensors at the GRO Chile Seismic Network

NASA Astrophysics Data System (ADS)

Farrell, M. E.; Russo, R. M.

2013-12-01

The installation of Earthscope Transportable Array-style geophysical observatories in Chile expands open data seismic recording capabilities in the southern hemisphere by nearly 30%, and has nearly tripled the number of seismic stations providing freely-available data in southern South America. Through the use of collocated seismic and atmospheric sensors at these stations we are able to analyze how local atmospheric conditions generate seismic noise, which can degrade data in seismic frequency bands at stations in the ';roaring forties' (S latitudes). Seismic vaults that are climate-controlled and insulated from the local environment are now employed throughout the world in an attempt to isolate seismometers from as many noise sources as possible. However, this is an expensive solution that is neither practical nor possible for all seismic deployments; and also, the increasing number and scope of temporary seismic deployments has resulted in the collection and archiving of terabytes of seismic data that is affected to some degree by natural seismic noise sources such as wind and atmospheric pressure changes. Changing air pressure can result in a depression and subsequent rebound of Earth's surface - which generates low frequency noise in seismic frequency bands - and even moderate winds can apply enough force to ground-coupled structures or to the surface above the seismometers themselves, resulting in significant noise. The 10 stations of the permanent Geophysical Reporting Observatories (GRO Chile), jointly installed during 2011-12 by IRIS and the Chilean Servicio Sismológico, include instrumentation in addition to the standard three seismic components. These stations, spaced approximately 300 km apart along the length of the country, continuously record a variety of atmospheric data including infrasound, air pressure, wind speed, and wind direction. The collocated seismic and atmospheric sensors at each station allow us to analyze both datasets together, to gain insight into how local atmospheric conditions couple with the ground to generate seismic noise, and to explore strategies for reducing this noise post data collection. Comparison of spectra of atmospheric data streams to the three broadband seismic channels for continuous signals recorded during May and June of 2013 shows high coherence between infrasound signals and time variation of air pressure (dP/dt) that we calculated from the air pressure data stream. Coherence between these signals is greatest for the east-west component of the seismic data in northern Chile. Although coherence between seismic, infrasound, and dP/dt is lower for all three seismic channels at other GRO Chile stations, for some of the data streams coherence can jump as much as 6 fold for certain frequency bands, with a common 3-fold increase for periods shorter than 10 seconds and the occasional 6-fold increase at long or very long periods.

Flat-slab subduction, whole crustal faulting, and geohazards in Alaska: Targets for Earthscope

NASA Astrophysics Data System (ADS)

Gulick, S. P.; Pavlis, T. L.; Bruhn, R. L.; Christeson, G. L.; Freymueller, J. T.; Hansen, R. A.; Koons, P. O.; Pavlis, G. L.; Roeske, S.; Reece, R.; van Avendonk, H. J.; Worthington, L. L.

2010-12-01

Crustal structure and evolution illuminated by the Continental Dynamics ST. Elias Erosion and tectonics Project (STEEP) highlights some fundamental questions about active tectonics processes in Alaska including: 1) what are the controls on far field deformation and lithospheric stabilization, 2) do strike slip faults extend through the entire crust and upper mantle and how does this influence mantle flow, and 3) how does the transition from “normal” subduction of the Pacific along the Aleutians to flat slab subduction of the Yakutat Terrane beneath southeast and central Alaska to translation of the Yakutat Terrane past North American in eastern Alaska affect geohazard assessment for the north Pacific? Active and passive seismic studies and geologic fieldwork focusing on the Yakutat Terrane show that the Terrane ranges from 15-35 km thick and is underthrusting the North American plate from the St. Elias Mountains to the Alaska Range (~500 km). Deformation of the upper plate occurs within the offshore Pamplona Zone fold and thrust belt, and onshore throughout the Robinson Mountains. Deformation patterns, structural evolution, and the sedimentary products of orogenesis are fundamentally influenced by feedbacks with glacial erosion. The Yakutat megathrust extends beneath Prince William Sound such that the 1964 Mw 9.2 great earthquake epicenter was on this plate boundary and jumped to the adjacent Aleutian megathrust coseismically; this event illuminates the potential for transitional tectonic systems to enhance geohazards. The northern, southern, and eastern limits of the Yakutat microplate are strike-slip faults that, where imaged, appear to cut the entire crustal section and may allow for crustal extrusion towards the Bering Sea. Yakutat Terrane effects on mantle flow, however, have been suggested to cross these crustal features to allow for far-field deformation in the Yukon, Brooks Range, and Amerasia Basin. From the STEEP results it is clear that the Yakutat Terrane is driving a range of tectonic and surface processes perturbing the Aleutian subduction system at its eastern extent and linking this system with Laramide style subduction and plate boundary strike-slip tectonics farther east. Targeted geodetic and seismic deployments as part of Earthscope could examine all of these features and seek to address fundamental questions about tectonic interactions.

Detailed study of upper mantle anisotropy in the upper mantle of eastern North America

NASA Astrophysics Data System (ADS)

Chen, X.; Levin, V. L.; Li, Y.

2016-12-01

We collected observations of core-refracted shear waves on a 1300 km long array crossing the eastern part of the North American continent from James Bay to the Fundy Basin. We combine data from the Earthscope Transportable Array, Canadian and US permanent observatories, and the recently completed Earthscope FlexArray QMIII.Past studies found ample evidence for directional dependence (anisotropy) of seismic wave speed in the upper mantle of this region. However, to date the lateral spacing of seismic observatories made direct comparisons between anisotropic structure and tectonic divisions evident on the surface challenging. With instruments spacing 50 km, and less near major tectonic boundaries such as the Grenville Front and the Appalachian Front, we can discriminate between gradual changes in anisotropic properties due to asthenospheric flow variations, and abrupt and localized changes likely to arise from juxtaposition of distinct lithospheric blocks.To insure lateral consistency of measurements we selected core-refracted shear waves that were observed over the entire length of our array. Also, since directional dependence of splitting parameters is a well recognized signature of vertical changes in anisotropic properties we examine observations from different directions, and look for systematic changes.Most locations show evidence for some degree of splitting in observed shear waves. Delays between fast and slow components estimated using rotation-correlation method range from 0.3 to 1.5 s. At most sites delay values vary considerably between individual phases measured. Fast polarizations are predominantly NE-SW, which agrees with numerous past studies of the region. Systematic directional dependence of fast polarization is seen at all sites we studied. Furthermore, the values of fast polarization appear to be similar along the entire array for individual events but vary from event to event. Both of these observations are consistent with the previously proposed notion of layered anisotropy in the upper mantle of the North American continent. We find localized changes in splitting parameters at the Grenville Front. The Appalachian Front, or the internal divisions of the Appalachian Orogen do not have obvious changes in splitting parameters associated with them.

The relationship between seismicity and wastewater injection in Johnson County, TX

NASA Astrophysics Data System (ADS)

Lee, S. S.; Walter, J. I.; Frohlich, C.; DeShon, H. R.

2015-12-01

In light of recent research that suggests some high-rate wastewater injection wells from commercial oil and gas operations are casually linked to recent earthquakes in North Texas and Oklahoma, we apply a waveform cross-correlation technique to continuous waveform data from 38 seismic stations across Texas and Oklahoma using templates from 96 cataloged events from 2010-2015. We focus on an area near Venus TX, 40 km south of the Dallas-Fort Worth metropolitan area in Johnson County where a M4.0 earthquake was reported by the USGS on 7 May 2015. The epicenter was within several km of 4 high rate wells with max injection rates ranging between 684,000-833,000 barrels/month. Templates were chosen from the USGS and locally derived Venus aftershock sequence, events in the ANSS catalog with a minimum magnitude of 2 between 2009-2015, and previously located earthquakes recorded by USArray stations between 2009-2011. In Johnson County, there are 27 wastewater injection wells, each with a reported maximum injection rate of 104,000 barrels/month and greater. We detected 494 events within Johnson and adjacent counties, with approximately 36% of the detections occurring within 10 km of the Venus earthquake, spanning March 2010 to June 2015. Most of the seismicity occurs adjacent to higher rate injection wells, suggesting a link between monthly injection rate and earthquake occurrence. Template matching allows us to detect earthquakes otherwise too small to be picked up by routine earthquake identification methods and informs our research concerning the presence and spatial distribution of possibly induced, small magnitude earthquakes. We plan to apply this technique to detect seismicity that may have occurred prior to the start of wastewater injection or felt earthquakes.

The ISC Contribution to Monitoring Research

NASA Astrophysics Data System (ADS)

Storchak, D. A.; Bondar, I.; Harris, J.; Gaspà Rebull, O.

2010-12-01

The International Seismological Centre (ISC) is a non-governmental organization charged with production of the ISC Bulletin - the definitive global summary of seismicity based on reports from over 4.5 thousand seismic stations worldwide. The ISC data have been extensively used in preparation of the Comprehensive Test Ban Treaty (CTBT). They are now used by the CTBTO Preparatory Technical Secretariat (PTS) and the State Parties as an important benchmark for assessing and monitoring detection capabilities of the International Monitoring System (IMS). The ISC also provides a valuable collection of reviewed waveform readings at academic and operational sites co-located with the IMS stations. To improve the timeliness of its Bulletin, the ISC is making a special effort in collecting preliminary bulletins from a growing number of networks worldwide that become available soon after seismic events occur. Preliminary bulletins are later substituted with the final analysis data once these become available to the ISC from each network. The ISC also collects and maintains data sets that are useful for monitoring research. These are the IASPEI Reference Event List of globally distributed GT0-5 events, the groomed ISC bulletin (EHB), the IDC REB, USArray phase picking data. In cooperation with the World Data Center for Seismology, Denver (USGS), the ISC also maintains the International Seismographic Station Registry that holds parameters of seismic stations used in the international data exchange. The UK Foreign and Commonwealth Office along with partners from several Nordic countries are currently funding a project to make the ISC database securely linked with the computer facilities at PTS and National Data Centres. The ISC Bulletin data are made available via a dedicated software link designed to offer the ISC data in a way convenient to monitoring community.

Accessing the uncertainties of seismic velocity and anisotropy structure of Northern Great Plains using a transdimensional Bayesian approach

NASA Astrophysics Data System (ADS)

Gao, C.; Lekic, V.

2017-12-01

Seismic imaging utilizing complementary seismic data provides unique insight on the formation, evolution and current structure of continental lithosphere. While numerous efforts have improved the resolution of seismic structure, the quantification of uncertainties remains challenging due to the non-linearity and the non-uniqueness of geophysical inverse problem. In this project, we use a reverse jump Markov chain Monte Carlo (rjMcMC) algorithm to incorporate seismic observables including Rayleigh and Love wave dispersion, Ps and Sp receiver function to invert for shear velocity (Vs), compressional velocity (Vp), density, and radial anisotropy of the lithospheric structure. The Bayesian nature and the transdimensionality of this approach allow the quantification of the model parameter uncertainties while keeping the models parsimonious. Both synthetic test and inversion of actual data for Ps and Sp receiver functions are performed. We quantify the information gained in different inversions by calculating the Kullback-Leibler divergence. Furthermore, we explore the ability of Rayleigh and Love wave dispersion data to constrain radial anisotropy. We show that when multiple types of model parameters (Vsv, Vsh, and Vp) are inverted simultaneously, the constraints on radial anisotropy are limited by relatively large data uncertainties and trade-off strongly with Vp. We then perform joint inversion of the surface wave dispersion (SWD) and Ps, Sp receiver functions, and show that the constraints on both isotropic Vs and radial anisotropy are significantly improved. To achieve faster convergence of the rjMcMC, we propose a progressive inclusion scheme, and invert SWD measurements and receiver functions from about 400 USArray stations in the Northern Great Plains. We start by only using SWD data due to its fast convergence rate. We then use the average of the ensemble as a starting model for the joint inversion, which is able to resolve distinct seismic signatures of geological structures including the trans-Hudson orogen, Wyoming craton and Yellowstone hotspot. Various analyses are done to access the uncertainties of the seismic velocities and Moho depths. We also address the importance of careful data processing of receiver functions by illustrating artifacts due to unmodelled sediment reverberations.

Earthquake source parameter and focal mechanism estimates for the Western Quebec Seismic Zone in eastern Canada

NASA Astrophysics Data System (ADS)

Rodriguez Padilla, A. M.; Onwuemeka, J.; Liu, Y.; Harrington, R. M.

2017-12-01

The Western Quebec Seismic Zone (WQSZ) is a 160-km-wide band of intraplate seismicity extending 500 km from the Adirondack Highlands (United States) to the Laurentian uplands (Canada). Historically, the WQSZ has experienced over fifteen earthquakes above magnitude 5, with the noteworthy MN5.2 Ladysmith event on May 17, 2013. Previous studies have associated seismicity in the area to the reactivation of Early Paleozoic normal faults within a failed Iapetan rift arm, or strength contrasts between mafic intrusions and felsic rocks due to the Mesozoic track of the Great Meteor hotspot. A good understanding of seismicity and its relation to pre-existing structures requires information about event source properties, such as static stress drop and fault plane orientation, which can be constrained via spectral analysis and focal mechanism solutions. Using data recorded by the CNSN and USArray Transportable Array, we first characterize b-value for 709 events between 2012 and 2016 in WQSZ, obtaining a value of 0.75. We then determine corner frequency and seismic moment values by fitting S-wave spectra on transverse components at all stations for 35 events MN 2.7+. We select event pairs with highly similar waveforms, proximal hypocenters, and magnitudes differing by 1-2 units. Our preliminary results using single-station spectra show corner frequencies of 15 to 40 Hz and stress drop values between 7 and 130 MPa, typical of intraplate seismicity. Last, we solve focal mechanism solutions of 35 events with impulsive P-wave arrivals at a minimum of 8 stations using the hybridMT moment tensor inversion algorithm. Our preliminary results suggest predominantly thrust faulting mechanisms, and at times oblique thrust faulting. The P-axis trend of the focal mechanism solutions suggests a principal stress orientation of NE-SW, which is consistent with that derived from focal mechanisms of earthquakes prior to 2013. We plan to fit the event pair spectral ratios to correct for attenuation effects and more accurately constrain the corner frequency values which can lead to more accurate static stress drop estimates, particularly of the larger events within an event pair.

Observations and interpretation of fundamental mode Rayleigh wavefields recorded by the Transportable Array (USArray)

USGS Publications Warehouse

Pollitz, F.F.

2008-01-01

Broadband recordings of the dense Transportable Array (TA) in the western United States provide unparalleled detailed images of long-period seismic surface wavefields. With 400 stations spanning most of the western United States, wavefronts of fundamental mode Rayleigh waves may be visualized coherently across the array at periods ???40 s. In order to constrain the Rayleigh wave phase velocity structure in the western United States, I assemble a data set of vertical component seismograms from 53 teleseismic events recorded by the TA from April 2006 to October 2007. Complex amplitude spectra from these recordings at peni ods 27-100 s are interpreted using the multiplane wave tomographic method of Friederich and Wielandt (1995) and Pollitz (1999). This analysis yields detailed surface wave phase velocity and three-dimensional shear wave velocity patterns across the North American plate boundary zone, elucidating the active processes in the highly heterogeneous western U.S. upper mantle.

Geophysical Data Define Boundaries and Sub-Regions of the Northern Gulf of Mexico Basin: Structural Histories and Causes are Hypothesized.

NASA Astrophysics Data System (ADS)

Kinsland, G. L.

2017-12-01

Within the last several years new types of geophysical data of the southern margin of the North American Craton and the Northern Gulf of Mexico Basin (NGoMB) have become available, e.g., results from the USArray experiment, high resolution satellite gravity data of the GoM itself and new heat flow data. These data when combined with previously existing geophysical data (gravity, magnetic and seismic) and shallow structural data offer new insights into the boundaries and sub-regions of the NGoMB. I offer hypotheses for the development of the structures of the buried crust and upper mantle which cause these features. Of particular interest might be my suggestion that the NGoMB might have extended in a southeasterly direction prior to the counter-clockwise rotation of the Yucatan Peninsula which ultimately resulted in the GoM.

Seismic shear waves as Foucault pendulum

NASA Astrophysics Data System (ADS)

Snieder, Roel; Sens-Schönfelder, Christoph; Ruigrok, Elmer; Shiomi, Katsuhiko

2016-03-01

Earth's rotation causes splitting of normal modes. Wave fronts and rays are, however, not affected by Earth's rotation, as we show theoretically and with observations made with USArray. We derive that the Coriolis force causes a small transverse component for P waves and a small longitudinal component for S waves. More importantly, Earth's rotation leads to a slow rotation of the transverse polarization of S waves; during the propagation of S waves the particle motion behaves just like a Foucault pendulum. The polarization plane of shear waves counteracts Earth's rotation and rotates clockwise in the Northern Hemisphere. The rotation rate is independent of the wave frequency and is purely geometric, like the Berry phase. Using the polarization of ScS and ScS2 waves, we show that the Foucault-like rotation of the S wave polarization can be observed. This can affect the determination of source mechanisms and the interpretation of observed SKS splitting.

Enhancement of EarthScope Infrastructure with Real Time Seismogeodesy

NASA Astrophysics Data System (ADS)

Bock, Y.; Melgar, D.; Geng, J.; Haase, J. S.; Crowell, B. W.; Squibb, M. B.

2013-12-01

Recent great earthquakes and ensuing tsunamis in Sumatra, Chile and Japan have demonstrated the need for accurate ground displacements that fully characterize the great amplitudes and broad dynamic range of motions associated with these complex ruptures. Our ability to model the source processes of these events and their effects, whether in real-time or after the fact, is limited by the weaknesses of both seismic and geodetic networks. Geodetic instruments provide the static component as well as coarse dynamic motions but are much less precise than seismic instruments, especially in the vertical direction. Seismic instruments provide exceptionally-sensitive dynamic motions but typically have difficulty in recovering unbiased near-field low-frequency absolute displacements. We have shown in several publications that an optimal combination of data from collocated GPS and strong motion accelerometers provides seismogeodetic displacement, velocity and point tilt waveforms spanning the full spectrum of seismic motion, without clipping and magnitude saturation. These observations are suitable for earthquake early warning (EEW) through detection of P wave arrivals, rapid assessment of earthquake magnitude, finite-source centroid moment tensor solutions and fault slip models, and tsunami warning, in particular in the near-source regions of large earthquakes. At present, more than 550 real-time GPS stations are operating in Western North America, a majority as part of the EarthScope/PBO effort with a concentration in the Cascadia region and southern California. Unfortunately, there are few collocations of GPS and accelerometers in this region (the exception being in parts of the BARD network in northern California). We have leveraged the considerable infrastructure already invested in the EarthScope project, and funding through NSF and NASA to create advanced software, hardware, and algorithms that make it possible to utilize EarthScope/PBO as an EEW test bed. We have developed cost-effective hardware and embedded firmware to upgrade existing real-time GPS stations with low-cost MEMS accelerometers. Fifteen PBO and SCIGN stations in southern California have already been upgraded with this technology. We have also developed a software suite to analyze seismogeodetic data in real time using a tightly-coupled precise point positioning (PPP) Kalman filter that supports PPP with ambiguity resolution (PPP-AR) throughout the seismically active regions of the Western U.S. The seismogeodetic system contributes directly to collaborative natural hazards research by providing technology for early warning systems for earthquakes, volcanoes and tsunamis, and for short-term high impact weather forecasting and related flooding hazards (we are also installing MEMS temperature and pressure sensors for GPS meteorology). The systems have also been deployed for earthquake engineering research for large structures (e.g., bridges, buildings, dams). Here we present the components and status of our seismogeodetic earthquake and tsunami monitoring system. Although the analysis techniques are quite advanced, the project lends itself to opportunities for education and outreach, specifically in illustrating concepts in elementary physics of position, velocity, and acceleration. Many of the animations generated in the research are available for development into appealing and accessible educational modules.

Detecting Noisy Events Using Waveform Cross-Correlation at Superarrays of Seismic Stations

NASA Astrophysics Data System (ADS)

von Seggern, D. H.; Tibuleac, I. M.

2007-12-01

Cross-correlation using master events, followed by stacking of the correlation series, has been shown to dramatically improve detection thresholds of small-to-medium seismic arrays. With the goal of lowering the detection threshold, determining relative magnitudes or moments, and characterizing sources by empirical Green's functions, we extend the cross-correlation methodology to include "superarrays" of seismic stations. The superarray concept naturally brings further benefits over conventional arrays and single-stations due to the fact that many distances and azimuths can be sampled. This extension is straightforward given the ease with which regional or global data from various stations or arrays can be currently accessed and combined into a single database. We demonstrate the capability of superarrays to detect and analyze events which lie below the detection threshold. This is aided by applying an F-statistic detector to the superarray cross-correlation stack and its components. Our first example illustrates the use of a superarray consisting of the Southern Great Basin Digital Seismic Network, a small-aperture array (NVAR) in Mina, Nevada and the Earthscope Transportable Array to detect events in California-Nevada areas. In our second example, we use a combination of small-to-medium arrays and single stations to study the rupture of the great Sumatra earthquake of 26 December 2004 and to detect its early aftershocks. The location and times of "detected" events are confirmed using a frequency- wavenumber method at the small-to-medium arrays. We propose that ad hoc superarrays can be used in many studies where conventional approaches previously used only single arrays or groups of single stations. The availability of near-real-time data from many networks and of archived data from, for instance, IRIS makes possible the easy assembly of superarrays. Furthermore, the continued improvement of seismic data availability and the continued growth in the number of world-wide seismic sensors will increasingly make superarrays an attractive choice for many studies.

Two-layer Crustal Structure of the Contiguous United States from Joint Inversion of USArray Receiver Functions and Gravity

NASA Astrophysics Data System (ADS)

Ma, X.; Lowry, A. R.

2015-12-01

The composition and thickness of crustal layering is fundamental to understanding the evolution and dynamics of continental lithosphere. Lowry and Pérez-Gussinyé (2011) found that the western Cordillera of the United States, characterized by active deformation and high heat flow, is strongly correlated with low bulk crustal seismic velocity ratio. They interpreted this observation as evidence that quartz controls continental tectonism and deformation. We will present new imaging of two-layer crustal composition and structure from cross-correlation of observed receiver functions and model synthetics. The cross-correlation coefficient of the two-layer model increases significantly relative to an assumed one-layer model, and the lower crustal thickness map from raw two-layer modeling (prior to Bayesian filtering with gravity models and Optimal Interpolation) clearly shows Colorado plateau and Appalachian boundaries, which are not apparent in upper crustal models, and also the high vP/vS fill the most of middle continental region while low vP/vS are on the west and east continental edge. In the presentation, we will show results of a new algorithm for joint Bayesian inversion of thickness and vP/vS of two-layer continental crustal structure. Recent thermodynamical modeling of geophysical models based on lab experiment data (Guerri et al., 2015) found that a large impedance contrast can be expected in the midcrust due to a phase transition that decreases plagioclase and increases clinopyroxene, without invoking any change in crustal chemistry. The depth of the transition depends on pressure, temperature and hydration, and in this presentation we will compare predictions of layer thicknesses and vP/vS predicted by mineral thermodynamics to those we observe in the USArray footprint.

Tomography of Pg and Sg Across the Western United States Using USArray Data

NASA Astrophysics Data System (ADS)

Steck, L.; Phillips, W. S.; Begnaud, M. L.; Stead, R.

2009-12-01

In this paper we explore the use of Pg and Sg for determining crustal structure in the western United States. Seismic data used in the study come from USArray, along with local and regional networks in the region. To invert the travel times for velocity structure we use the LSQR algorithm assuming a great circle arc path between source and receiver. First difference smoothing is used to regularize the model and we calculate station and event terms. For Pg we have about 160,000 arrivals from 30,000 events reporting at 1500 stations. If we trim data based on an epicentral ground truth level of 25 km or better, we have 53000 arrivals, 5000 events and 1300 stations. Data density is such that grids of 0.5 deg or better are possible. Velocity results show good correlation with tectonic provinces. We find fast velocities beneath the Snake River Plain, coastal Washington State, and for the coast ranges of California south of Point Reyes. Low velocities are observed on the border between Idaho and Montana, and in the Basin and Range of eastern Nevada, southeastern California, and southern Arizona. For Sg we have 48,813 arrivals for 13,548 events at 1052 stations, not filtering by ground truth level. Excellent coverage allows grids to 0.5 deg or lower. Prominent features of this model include high velocities in the Snake River Plain, Colorado Plateau, and the Cascades and Sierra Nevada. Low velocities are found in Southern California, the Basin and Range, and the Columbia Plateau. Root-mean-square residual reductions are 34% for Pg and 41% for Sg.

Stress concentration on Intraplate Seismicity: Numerical Modeling of Slab-released Fluids in the New Madrid Seismic Zone

NASA Astrophysics Data System (ADS)

Saxena, A.; Choi, E.; Powell, C. A.

2017-12-01

The mechanism behind the seismicity of the New Madrid Seismic Zone (NMSZ), the major intraplate earthquake source in the Central and Eastern US (CEUS), is still debated but new insights are being provided by recent tomographic studies involving USArray. A high-resolution tomography study by Nyamwandha et al. (2016) in the NMSZ indicates the presence of low (3 % - 5 %) upper mantle Vp and Vs anomalies in the depth range 100 to 250 km. The elevated anomaly magnitudes are difficult to explain by temperature alone. As the low-velocity anomalies beneath the northeast China are attributed to fluids released from the stagnant Pacific slab, water released from the stagnant Laramide Slab, presently located at transition zone depths beneath the CEUS might be contributing to the low velocity features in this region's upper mantle. Here, we investigate the potential impact of the slab-released fluids on the stresses at seismogenic depths using numerical modeling. We convert the tomographic results into temperature field under various assumed values of spatially uniform water content. In more realistic cases, water content is added only when the converted temperature exceeds the melting temperature of olivine. Viscosities are then computed based on the temperature and water content and given to our geodynamic models created by Pylith, an open source software for crustal dynamics. The model results show that increasing water content weakens the upper mantle more than temperature alone and thus elevates the differential stress in the upper crust. These results can better explain the tomography results and seismicity without invoking melting. We also invert the tomography results for volume fraction of orthopyroxene and temperature and compare the resultant stresses with those for pure olivine. To enhance the reproducibility, selected models in this study will be made available in the form of sharable and reproducible packages enabled by EarthCube Building block project, GeoTrust.

Detecting lower-mantle slabs beneath Asia and the Aleutians

NASA Astrophysics Data System (ADS)

Schumacher, L.; Thomas, C.

2016-06-01

To investigate the descend of subducted slabs we search for and analyse seismic arrivals that reflected off the surface of the slab. In order to distinguish between such arrivals and other seismic phases, we search for waves that reach a seismic array with a backazimuth deviating from the theoretical backazimuth of the earthquake. Source-receiver combinations are chosen in a way that their great circle paths do not intersect the slab region, hence the direct arrivals can serve as reference. We focus on the North and Northwest Pacific region by using earthquakes from Japan, the Philippines and the Hindu Kush area recorded at North American networks (e.g. USArray, Alaska and Canada). Using seismic array techniques for analysing the data and record information on slowness, backazimuth and traveltime of the observed out-of-plane arrivals we use these measurements to trace the wave back through a 1-D velocity model to its scattering/reflection location. We find a number of out-of-plane reflections. Assuming only single scattering, most out-of-plane signals have to travel as P-to-P phases and only a few as S-to-P phases, due to the length of the seismograms we processed. The located reflection points present a view of the 3-D structures within the mantle. In the upper mantle and the transition zone they correlate well with the edges of fast velocity regions in tomographic images. We also find reflection points in the mid- and lower mantle and their locations generally agree with fast velocities mapped by seismic tomography models suggesting that in the subduction regions we map, slabs enter the lower mantle. To validate our approach, we calculate and process synthetic seismograms for 3-D wave field propagation through a model containing a slab-like heterogeneity. We show, that depending on the source-receiver geometry relative to the reflection plane, it is indeed possible to observe and back-trace out-of-plane signals.

Resolving the tectonic transition between ancestral North America and the northern Cordillera

NASA Astrophysics Data System (ADS)

Schaeffer, A. J.; Audet, P.; Lebedev, S.

2015-12-01

The northern Cordillera, situated in the Canadian northwest, is one of the most actively deforming regions in Canada and host to the highest earthquake activity in the country. Furthermore, it presents a largely contiguous snapshot through almost 4 Gyr of Earth's history across a zone <2000 km in linear extent. Deformation is thought to be driven by tectonic forces transferred from the Alaska-Pacific plate collision eastwards to the Cordilleran Deformation Front (CDF), where the westward edge of the Canadian Shield acts as a rigid backstop. Past studies in the southern Yukon indicate a sharp transition into the craton underlying the CDF and evidence of craton growth through shallow subduction. Further north the proximity of the craton edge to the CDF remains largely unresolved; based on studies of the southern Cordillera and Alaska, significant variations in lithospheric architecture are expected. Additionally, significant seismicity is observed further north off the Beaufort Shelf; however, its relationship to the regional stress fields and associated tectonic forcing is unclear. Despite the high seismicity levels across, detailed study of this region has been limited by insufficient coverage of seismological infrastructure, hindering resolution in past models. With the deployment of the USArray Transportable Array in Alaska over the last several years, combined with regional arrays such as the Yukon-Northwest Seismic Network (YNSN), Banks Island Seismic Network (BISN) and Mackenzie Mountains Experiment, new studies will leverage these datasets enabling more detailed imaging of the structure and seismicity across the region. Here we present a new high-resolution, vertically polarized shear speed and azimuthal model of northwestern Canada and Alaska, constrained by vertical component seismogram fits computed using the Automated Multimode Inversion of Surface, S, and multiple-S waveforms. With this new model, we aim to address key questions relating to the dynamics of the northern Cordillera, including how far west the craton edge extends at depth, in addition to the crustal thickness, velocity structure, and pattern of crustal fabrics around major faults throughout the region.

Updates to FuncLab, a Matlab based GUI for handling receiver functions

NASA Astrophysics Data System (ADS)

Porritt, Robert W.; Miller, Meghan S.

2018-02-01

Receiver functions are a versatile tool commonly used in seismic imaging. Depending on how they are processed, they can be used to image discontinuity structure within the crust or mantle or they can be inverted for seismic velocity either directly or jointly with complementary datasets. However, modern studies generally require large datasets which can be challenging to handle; therefore, FuncLab was originally written as an interactive Matlab GUI to assist in handling these large datasets. This software uses a project database to allow interactive trace editing, data visualization, H-κ stacking for crustal thickness and Vp/Vs ratio, and common conversion point stacking while minimizing computational costs. Since its initial release, significant advances have been made in the implementation of web services and changes in the underlying Matlab platform have necessitated a significant revision to the software. Here, we present revisions to the software, including new features such as data downloading via irisFetch.m, receiver function calculations via processRFmatlab, on-the-fly cross-section tools, interface picking, and more. In the descriptions of the tools, we present its application to a test dataset in Michigan, Wisconsin, and neighboring areas following the passage of USArray Transportable Array. The software is made available online at https://robporritt.wordpress.com/software.

Prototype PBO Instrumentation of CALIPSO Project Captures World-Record Lava Dome Collapse on Montserrat Volcano

NASA Astrophysics Data System (ADS)

Mattioli, Glen S.; Young, Simon R.; Voight, Barry; Sparks, R. Steven J.; Shalev, Eylon; Selwyn, Sacks; Malin, Peter; Linde, Alan; Johnston, William; Hadayat, Dannie; Elsworth, Derek; Dunkley, Peter; Herd, Richard; Neuberg, Jurgen; Norton, Gillian; Widiwijayanti, Christina

2004-08-01

This article is an update on the status of an innovative new project designed to enhance generally our understanding of andesitic volcano eruption dynamics and, specifically, the monitoring and scientific infrastructure at the active Soufriàre Hills Volcano (SHV), Montserrat. The project has been designated as the Caribbean Andesite Lava Island Precision Seismo-geodetic Observatory, known as CALIPSO. Its purpose is to investigate the dynamics of the entire SHV magmatic system using an integrated array of specialized instruments in four strategically located ~200-m-deep boreholes in concert with several shallower holes and surface sites. The project is unique, as it represents the first, and only, such borehole volcano-monitoring array deployed at an andesitic stratovolcano. CALIPSO may be considered as a prototype for planned Plate Boundary Observatory (PBO) installations at several volcanic targets in the western United States. Scientific objectives of the EarthScope Integrated Science Plan (ES-ISP) relevant to magmatic systems are to investigate (1) melt generation in the mantle; (2) melt migration from the mantle to and through the crust to the surface; (3) melt residence times at various deep reservoirs; and (4) delineation of characteristic patterns of surface deformation and seismicity, which may prove useful in eruption forecasting. The CALIPSO project shares most of the same scientific goals and has, moreover, the benefit of a rich existing geophysical context in its deployment at SHV. Our experience during instrument design, planning, drilling and installation, systems integration, and early operation of CALIPSO, moreover, may prove valuable to EarthScope and PBO managers.

Imaging Basin Structure with Teleseismic Virtual Source Reflection Profiles

NASA Astrophysics Data System (ADS)

Yang, Z.; Sheehan, A. F.; Yeck, W. L.; Miller, K. C.; Worthington, L. L.; Erslev, E.; Harder, S. H.; Anderson, M. L.; Siddoway, C. S.

2011-12-01

We demonstrate a case of using teleseisms recorded on single channel high frequency geophones to image upper crustal structure across the Bighorn Arch in north-central Wyoming. The dataset was obtained through the EarthScope FlexArray Bighorn Arch Seismic Experiment (BASE). In addition to traditional active and passive source seismic data acquisition, BASE included a 12 day continuous (passive source) deployment of 850 geophones with 'Texan' dataloggers. The geophones were deployed in three E-W lines in north-central Wyoming extending from the Powder River Basin across the Bighorn Mountains and across the Bighorn Basin, and two N-S lines on east and west flanks of the Bighorn Mountains. The station interval is roughly 1.5-2 km, good for imaging coherent shallow structures. The approach used in this study uses the surface reflection as virtual seismic source and reverberated teleseismic P-wave phase (PpPdp) (teleseismic P-wave reflected at receiver side free surface and then reflected off crustal seismic interface) to construct seismic profiles. These profiles are equivalent to conventional active source seismic reflection profiles except that high-frequency (up to 2.4 Hz) transmitted wave fields from distant earthquakes are used as sources. On the constructed seismic profiles, the coherent PpPdp phases beneath Powder River and Bighorn Basins are distinct after the source wavelet is removed from the seismograms by deconvolution. Under the Bighorn Arch, no clear coherent signals are observed. We combine phases PpPdp and Ps to constrain the averaged Vp/Vs: 2.05-2.15 for the Powder River Basin and 1.9-2.0 for the Bighorn Basin. These high Vp/Vs ratios suggest that the layers within which P-wave reverberates are sedimentary. Assuming Vp as 4 km/s under the Powder River Basin, the estimated thickness of sedimentary layer above reflection below the profile is 3-4.5 km, consistent with the depth of the top of the Tensleep Fm. Therefore we interpret the coherent PpPdp phases about 1-3 s after direct P-wave arrival as the reflections off the interface between the Paleozoic carbonates/sandstones and Mesozoic shales.

Attenuation of Lg in the western US using the USArray

NASA Astrophysics Data System (ADS)

Phillips, W. Scott; Stead, Richard J.

2008-04-01

The unprecedented breadth and density of the USArray allows us to resolve lateral variations of 1-Hz Lg attenuation to 0.5 degrees over much of the western United States. We collected over 31,000 Lg amplitudes from 547 events and 408 stations of the initial USArray footprint. Two-dimensional tomographic inversion yielded Q ranging from 60 to 550, with a variance reduction of 47% relative to the best-fit constant Q model (Q = 155). Q is low over most of the region, with lowest values associated with recent volcanic activity, and active shear zones. High Q is found in older, stable crust, notably the Colorado and Columbia plateaus, while smaller islands of high Q are associated with batholiths, including the Sierra Nevada, Peninsular, and Bitterroot Ranges, the western Mojave, and Okanogan Highlands, as well as other areas of competent crust such as the Harcuvar range, and two topographically bounded blocks in the Basin and Range.

The Cascadia Paradox: Understanding Mantle Flow in the Cascadia Subduction System

NASA Astrophysics Data System (ADS)

Long, M. D.

2015-12-01

The pattern of mantle flow in subduction systems, and the processes that control the mantle flow field, is a fundamental but still poorly understood aspect of subduction dynamics. Mantle flow plays a key role in controlling the transport of volatiles and melt in the wedge, deformation of the overriding plate, mass transfer between the upper and lower mantle, and the morphology and dynamics of slabs. The Cascadia subduction zone provides a compelling system in which to understand the controls on mantle flow, particularly given the dense geophysical observations provided by EarthScope, GeoPRISMS, the Cascadia Initiative, and related efforts. Cascadia is a particularly intriguing system because observations of seismic anisotropy, which provide relatively direct constraints on mantle flow, seem to yield contradictory views of the mantle flow field in different parts of the system. Observations of seismic anisotropy on the overriding plate apparently require a significant component of three-dimensional, toroidal flow around the slab edge, while new observations from offshore stations are compellingly explained with a simple two-dimensional entrained flow model. Recent evidence from seismic tomography for the fragmentation of the Cascadia slab at depth provides a further puzzle: how can a fragmented slab provide a driving force for either two-dimensional entrained flow or three-dimensional toroidal flow due to slab rollback? I will present a synthesis of recent observations of seismic anisotropy in the Cascadia subduction system, and how they can be integrated with constraints from geodynamical modeling, geochemistry, and the history and timing of Pacific Northwest volcanism. I will discuss the compelling but contradictory evidence for each of the endmember mantle flow models (two-dimensional entrained flow vs. three-dimensional toroidal flow) and explore possible avenues for resolving the Cascadia Paradox.

Control of the Lithospheric Mantle on intracontinental Deformation: Revival of Eastern U.S. Tectonism

NASA Astrophysics Data System (ADS)

Biryol, C. B.; Wagner, L. S.; Fischer, K. M.; Hawman, R. B.

2016-12-01

The present tectonic configuration of the southeastern United States is a product of earlier episodes of arc accretion, continental collision and breakup. This region is located in the interior of the North American Plate, some 1500 km away from closest active plate margin. However, there is ongoing tectonism across the area with multiple zones of seismicity, rejuvenation of the Appalachians of North Carolina, Virginia, and Pennsylvania, and Cenozoic intraplate volcanism. The mechanisms controlling this activity and the modern-day state of stress remain enigmatic. Two factors often regarded as major contributors are plate strength and preexisting inherited structures. Recent improvements in broadband seismic data coverage in the region associated with the South Eastern Suture of the Appalachian Margin Experiment (SESAME) and EarthScope Transportable Array make it possible to obtain detailed information on the structure of the lithosphere in the region. Here we present new tomographic images of the upper mantle beneath the Southeastern United States, revealing large-scale structural variations in the upper mantle. Our results indicate fast seismic velocity patterns that can be interpreted as ongoing lithospheric foundering. We observe an agreement between the locations of these upper mantle anomalies and the location of major zones of tectonism, volcanism and seismicity, providing a viable explanation for modern-day activity in this plate interior setting long after it became a passive margin. Based on distinct variations in the geometry and thickness of the lithospheric mantle and foundered lithosphere, we propose that piecemeal delamination has occurred beneath the region throughout the Cenozoic, removing a significant amount of reworked/deformed mantle lithosphere. Ongoing lithospheric foundering beneath the eastern margin of stable North America explains significant variations in thickness of lithospheric mantle across the former Grenville deformation front.

Guided Seismic Waves: Possible Diagnostics for Hot Plumes in the Mantle

NASA Astrophysics Data System (ADS)

Evans, J. R.; Julian, B. R.; Foulger, G. R.

2005-12-01

Seismic waves potentially provide by far the highest resolution view of the three-dimensional structure of the mantle, and the hope of detecting wave-speed anomalies caused by hot or compositionally buoyant mantle plumes has been a major incentive to the development of tomographic seismic techniques. Seismic tomography is limited, however, by the uneven geographical distribution of earthquakes and seismometers, which can produce artificial tomographic wave-speed anomalies that are difficult to distinguish from real structures in the mantle. An alternate approach may be possible, because hot plumes and possibly some compositional upwellings would have low seismic-wave speeds and would act as efficient waveguides over great depth ranges in the mantle. Plume-guided waves would be little affected by bends or other geometric complexities in the waveguides (analogously to French horns and fiber-optic cables), and their dispersion would make them distinctive on seismograms and would provide information on the size and structure of the waveguide. The main unanswered question is whether guided waves in plumes could be excited sufficiently to be observable. Earthquakes do not occur in the deep mantle, but at least two other possible sources of excitation can be imagined: (1) shallow earthquakes at or near plume-fed hotspots; and (2) coupling of plume-guided waves to seismic body waves near the bottom of the mantle. In the first case, downward-traveling guided waves transformed to seismic body waves at the bottom of the waveguide would have to be detected at teleseismic distances. In the second case, upward-traveling guided waves generated by teleseismic body waves would be detected on seismometers at hotspots. Qualitative reasoning based on considerations of reciprocity suggests that the signals in these two situations should be similar in size and appearance. The focusing of seismic core phases at caustics would amplify plume waves excited by either mechanism (1) or (2) at particular epicentral distances. A failure to find such guided waves experimentally could mean either that the waveguides (plumes) do not exist or that the excitation mechanisms and/or seismometer networks are inadequate. Distinguishing these two possibilities would require careful analysis. Anticipated major improvements in seismic instrumentation, such as the EarthScope initiative, make this a propitious time to undertake a search for plume-guided waves in the mantle.

What can we learn from the Wells, NV earthquake sequence about seismic hazard in the intermountain west?

USGS Publications Warehouse

Petersen, M.D.; Pankow, K.L.; Biasi, G.P.; Meremonte, M.

2008-01-01

The February 21, 2008 Wells, NV earthquake (M 6) was felt throughout eastern Nevada, southern Idaho, and western Utah. The town of Wells sustained significant damage to unreinforced masonry buildings. The earthquake occurred in a region of low seismic hazard with little seismicity, low geodetic strain rates, and few mapped faults. The peak horizontal ground acceleration predicted by the USGS National Seismic Hazard Maps is about 0.2 g at 2% probability of exceedance in 50 years, with the contributions coming mostly from the Ruby Mountain fault and background seismicity (M5-7.0). The hazard model predicts that the probability of occurrence of an M>6 event within 50 km of Wells is about 15% in 100 years. Although the earthquake was inside the USArray Transportable Array network, the nearest on-scale recordings of ground motions from the mainshock were too distant to estimate accelerations in town. The University of Nevada Reno, the University of Utah, and the U.S. Geological Survey deployed portable instruments to capture the ground motions from aftershocks of this rare normal-faulting event. Shaking from a M 4.7 aftershock recorded on portable instruments at distances less than 10 km exceeded 0.3 g, and sustained accelerations above 0.1 g lasted for about 5 seconds. For a magnitude 5 earthquake at 10 km distance the NGA equations predict median peak ground accelerations about 0.1 g. Ground motions from normal faulting earthquakes are poorly represented in the ground motion prediction equations. We compare portable and Transportable Array ground-motion recordings with prediction equations. Advanced National Seismic System stations in Utah recorded ground motions 250 km from the mainshock of about 2% g. The maximum ground motion recorded in Salt Lake City was in the center of the basin. We analyze the spatial variability of ground motions (rock vs. soil) and the influence of the Salt Lake Basin in modifying the ground motions. We then compare this data with the September 28, 2004 Parkfield aftershocks to contrast the differences between strike-slip and normal ground motions.

Receiver function and gravity constraints on crustal structure and vertical movements of the Upper Mississippi Embayment and Ozark Uplift

NASA Astrophysics Data System (ADS)

Liu, Lin; Gao, Stephen S.; Liu, Kelly H.; Mickus, Kevin

2017-06-01

The Upper Mississippi Embayment (UME), where the seismically active New Madrid Seismic Zone resides, experienced two phases of subsidence commencing in the Late Precambrian and Cretaceous, respectively. To provide new constraints on models proposed for the mechanisms responsible for the subsidence, we computed and stacked P-to-S receiver functions recorded by 49 USArray and other seismic stations located in the UME and the adjacent Ozark Uplift and modeled Bouguer gravity anomaly data. The inferred thickness, density, and Vp/Vs of the upper and lower crustal layers suggest that the UME is characterized by a mafic and high-density upper crustal layer of ˜30 km thickness, which is underlain by a higher-density lower crustal layer of up to ˜15 km. Those measurements, in the background of previously published geological observations on the subsidence and uplift history of the UME, are in agreement with the model that the Cretaceous subsidence, which was suggested to be preceded by an approximately 2 km uplift, was the consequence of the passage of a previously proposed thermal plume. The thermoelastic effects of the plume would have induced wide-spread intrusion of mafic mantle material into the weak UME crust fractured by Precambrian rifting and increased its density, resulting in renewed subsidence after the thermal source was removed. In contrast, the Ozark Uplift has crustal density, thickness, and Vp/Vs measurements that are comparable to those observed on cratonic areas, suggesting an overall normal crust without significant modification by the proposed plume, probably owing to the relatively strong and thick lithosphere.

Imaging paleoslabs in the D″ layer beneath Central America and the Caribbean using seismic waveform inversion.

PubMed

Borgeaud, Anselme F E; Kawai, Kenji; Konishi, Kensuke; Geller, Robert J

2017-11-01

D″ (Dee double prime), the lowermost layer of the Earth's mantle, is the thermal boundary layer (TBL) of mantle convection immediately above the Earth's liquid outer core. As the origin of upwelling of hot material and the destination of paleoslabs (downwelling cold slab remnants), D″ plays a major role in the Earth's evolution. D″ beneath Central America and the Caribbean is of particular geodynamical interest, because the paleo- and present Pacific plates have been subducting beneath the western margin of Pangaea since ~250 million years ago, which implies that paleoslabs could have reached the lowermost mantle. We conduct waveform inversion using a data set of ~7700 transverse component records to infer the detailed three-dimensional S-velocity structure in the lowermost 400 km of the mantle in the study region so that we can investigate how cold paleoslabs interact with the hot TBL above the core-mantle boundary (CMB). We can obtain high-resolution images because the lowermost mantle here is densely sampled by seismic waves due to the full deployment of the USArray broadband seismic stations during 2004-2015. We find two distinct strong high-velocity anomalies, which we interpret as paleoslabs, just above the CMB beneath Central America and Venezuela, respectively, surrounded by low-velocity regions. Strong low-velocity anomalies concentrated in the lowermost 100 km of the mantle suggest the existence of chemically distinct denser material connected to low-velocity anomalies in the lower mantle inferred by previous studies, suggesting that plate tectonics on the Earth's surface might control the modality of convection in the lower mantle.

Mantle circulation models with variational data assimilation: Inferring past mantle flow and structure from plate motion histories and seismic tomography

NASA Astrophysics Data System (ADS)

Bunge, Hans-Peter

2002-08-01

Earth's mantle overturns itself about once every 200 Million years (myrs). Prima facie evidence for this overturn is the motion of tectonic plates at the surface of the Earth driving the geologic activity of our planet. Supporting evidence also comes from seismic tomograms of the Earth's interior that reveal the convective currents in remarkable clarity. Much has been learned about the physics of solid state mantle convection over the past two decades aided primarily by sophisticated computer simulations. Such simulations are reaching the threshold of fully resolving the convective system globally. In this talk we will review recent progress in mantle dynamics studies. We will then turn our attention to the fundamental question of whether it is possible to explicitly reconstruct mantle flow back in time. This is a classic problem of history matching, amenable to control theory and data assimilation. The technical advances that make such approach feasible are dramatically increasing compute resources, represented for example through Beowulf clusters, and new observational initiatives, represented for example through the US-Array effort that should lead to an order-of-magnitude improvement in our ability to resolve Earth structure seismically below North America. In fact, new observational constraints on deep Earth structure illustrate the growing importance of of improving our data assimilation skills in deep Earth models. We will explore data assimilation through high resolution global adjoint models of mantle circulation and conclude that it is feasible to reconstruct mantle flow back in time for at least the past 100 myrs.

Magnetotelluric Investigations of Convergent Margins and of Incipient Rifting: Preliminary Results from the EarthScope MT Transportable Array and MT FlexArray Deployments in Cascadia and in the North American Mid-Continent Region

NASA Astrophysics Data System (ADS)

Schultz, A.; Bedrosian, P.; Key, K.; Livelybrooks, D.; Egbert, G. D.; Bowles-martinez, E.; Wannamaker, P. E.

2014-12-01

We report on preliminary analyses of data from the EarthScope MT Transportable Array, and from two high-resolution EarthScope MT studies in Cascadia. The first of these, iMUSH, is acquiring wideband MT data at 150 sites, as well as active and passive seismic data in SW Washington (including Mounts Saint Helens, Adams and Rainier). iMUSH seeks to determine details of crustal magma transport and storage, and to resolve major tectonic controls on volcanism along the arc. iMUSH may help to settle a debate over the origin of the SW Washington Crustal Conductor (SWCC), which covers ~5000 km2and that has alternately been attributed to accreted Eocene metasediments or to an extensive region of partial melt in the lower crust beneath the three volcanoes. The iMUSH array is continguous with an amphibious ~150 station MT experiment (MOCHA) onshore and offshore of the Washington and Oregon forearc. MOCHA iwill image the crust and upper mantle of the subduction system in 3D, constraining the fluid input to the system from offshore and the distribution of fluids released from the down-going slab, including along the transitional zone where Episodic Tremor and Slip occurs. Our goal is to refine our understanding of the segmentation, structure and fluid distribution along the convergent margin segments, and their relationship to the spatial pattern of ETS. In contrast to the active Cascadia margin, the Mid-Continent Rift (MCR) is the trace of a massive igneous event that nearly split North America 1.1 billion years ago. Initial results from 3D inversion of MT Transportable Array data show less fine-scale heterogeneity in the upper mantle (250 km depth) than is evident in western, tectonic North America, but a division at the base of thick lithosphere, with higher conductivities beneath and immediately south of the Great Lakes, than to the south. From the base of the lithosphere to the Moho, this high conductivity feature narrows, ultimately disappearing in the mid-crust. In the upper crust above this feature, an E-W elongated conductive feature appears that maps to surface expressions of the MCR. The significance of this deep feature, and its relationship to the failed rifting event of the mesoproterozoic era will be discussed.

A 3-D crustal and uppermost mantle model of the western US from receiver functions and surface wave dispersion derived from ambient noise and teleseismic earthquakes

NASA Astrophysics Data System (ADS)

Shen, W.; Schulte-Pelkum, V.; Ritzwoller, M. H.

2011-12-01

The joint inversion of surface wave dispersion and receiver functions was proven feasible on a station by station basis more than a decade ago. Joint application to a large number of stations across a broad region such as western US is more challenging, however, because of the different resolutions of the two methods. Improvements in resolution in surface wave studies derived from ambient noise and array-based methods applied to earthquake data now allow surface wave dispersion and receiver functions to be inverted simultaneously across much of the Earthscope/USArray Transportable Array (TA), and we have developed a Monte-Carlo procedure for this purpose. As a proof of concept we applied this procedure to a region containing 186 TA stations in the intermountain west, including a variety of tectonic settings such as the Colorado Plateau, the Basin and Range, the Rocky Mountains, and the Great Plains. This work has now been expanded to encompass all TA stations in the western US. Our approach includes three main components. (1) We enlarge the Earthscope Automated Receiver Survey (EARS) receiver function database by adding more events within a quality control procedure. A back-azimuth-independent receiver function and its associated uncertainties are constructed using a harmonic stripping algorithm. (2) Rayleigh wave dispersion curves are generated from the eikonal tomography applied to ambient noise cross-correlation data and Helmoholtz tomography applied to teleseismic surface wave data to yield dispersion maps from 8 sec to 80 sec period. (3) We apply a Metropolis Monte Carlo algorithm to invert for the average velocity structure beneath each station. Simple kriging is applied to interpolate to the discrete results into a continuous 3-D model. This method has now been applied to over 1,000 TA stations in the western US. We show that the receiver functions and surface wave dispersion data can be reconciled beneath more than 80% of the stations using a smooth parameterization of both crustal and uppermost mantle structure. After the inversion, a 3-D model for the crust and uppermost mantle to a depth of 150 km is constructed for this region. Compared with using surface wave data alone, uncertainty in crustal thickness is much lower and as a result, the lower crustal velocity is better constrained given a smaller depth-velocity trade-off. The new 3-D model including Moho depth with attendant uncertainties provides the basis for further analysis on radial anisotropy and geodynamics in the western US, and also forms a starting point for other seismological studies such as body wave tomography and receiver function CCP analysis.

SM1.3 Seismic Centers Data Acquisition: an introduction to Antelope, EarthWorm, SeisComP and their usage around the world

NASA Astrophysics Data System (ADS)

Pesaresi, Damiano; Sleeman, Reinoud

2010-05-01

Many medium to big size seismic data centers around the world are facing the same question: which software to use to acquire seismic data in real-time? A home-made or a commercial one? Both choices have pros and cons. The in-house development of software usually requires an increased investment in human resources rather than a financial investment. However, the advantage of fully accomplishing your own needs could be put in danger when the software engineer quits the job! Commercial software offers the advantage of being maintained, but it may require both a considerable financial investment and training. The main seismic software data acquisition suites available nowadays are the public domain SeisComP and EarthWorm packages and the commercial package Antelope. Nanometrics, Guralp and RefTek also provide seismic data acquisition software, but they are mainly intended for single station/network acquisition. Antelope is a software package for real-time acquisition and processing of seismic network data, with its roots in the academic seismological community. The software is developed by Boulder Real Time Technology (BRTT) and commercialized by Kinemetrics. It is used by IRIS affiliates for off-line data processing and it is the main acquisition tool for the USArray program and data centers in Europe like the ORFEUS Data Center, OGS (Italy), ZAMG (Austria), ARSO (Slovenia) and GFU (Czech Republic). SeisComP was originally developed for the GEOFON global network to provide a system for data acquisition, data exchange (SeedLink protocol) and automatic processing. It has evolved into to a widely distributed, networked seismographic system for data acquisition and real-time data exchange over Internet and is supported by ORFEUS as the standard seismic data acquisition tool in Europe. SeisComP3 is the next generation of the software and was developed for the German Indonesian Tsunami Early Warning System (GITEWS). SeisComP is licensed by GFZ (free of charge) and maintained by a private company (GEMPA). EarthWorm was originally developed by United States Geological Survey (USGS) to exchange data with the Canadian seismologists. Its is now used by several institution around the world. It is maintained and developed by a commercial software house, ISTI.

Joint inversion of surface wave dispersion and receiver functions for crustal structure in Oklahoma

NASA Astrophysics Data System (ADS)

Guo, Hao

The surge in seismicity in Oklahoma starting in 2008 raises questions about the actual locations of the earthquakes in the upper crust. The key to answering this is an improved crustal model that explains as many observations as possible. Love and Rayleigh wave dispersion, teleseismic P-wave receiver functions and some unique transverse motions observed at distances less than 100 km that are characteristics of rays reverberating in a basin provide data to derive the crustal model. The surface wave dispersion data set consists of over 300,000 Love/Rayleigh phase/group values obtained from ambient noise cross-correlation of BH channels of the 133 Transportable Array (TA) stations of Earthscope to periods as short as 2 seconds. Station coverage is dense enough to perform the tomography on a 25*25 km grid that should be able to image shallow geological structures. In addition, receiver functions were obtained using teleseismic data recorded from 3 US Geological Survey Networks (GS) stations and 6 Oklahoma Seismic Network (OK) stations from 2011 to 2014. The 1-D S-wave velocity models derived by the joint inversion of surface wave dispersion and receiver functions with geological constraints are tested by fitting the independent transverse seismograms. This test also provides constraints on the earthquake depths in relation to the geological structure.

Lg attenuation, frequency dependence and relative site response of the western United States as revealed by the EarthScope Transportable Array

NASA Astrophysics Data System (ADS)

Gallegos, Andrea; Ranasinghe, Nishath; Ni, James; Sandvol, Eric

2017-06-01

Lg attenuation of the western United States is estimated using regional waveforms recorded by EarthScope's Transportable Array, the Berkeley Digital Seismograph Network and the Caltech Regional Seismic Network. Lg attenuation is determined using the two-station method (TSM). 292 events ranging from magnitude 4 to 6.5 in a time range for the years between 2005 and 2010 are used. We have tomographically mapped variations in effective Lg Q at narrow bands with central frequencies of 0.5, 1, 2 and 3 Hz. The relative site responses of individual stations are determined using a reverse TSM at these central frequencies. Both the two-station and reverse TSMs have the advantage of effectively removing site and source effects without requiring a priori models while mapping lateral heterogeneities in the crust. Regions of high attenuation are found along the Snake River Plain, along the northern California-Oregon border, throughout the Basin and Range, Walker Lane, Wasatch Fault and the Rio Grande Rift. Regions of low attenuation are found in the Colorado Plateau, Rocky Mountains, central Nevada and the Columbia Plateau. Overall, Lg Q was found to have a power-law frequency dependence, with an increase in central frequency resulting in an increase in Q. Relative site responses were found to vary strongly with local geology. Hard rock areas such as the Sierra Nevada Mountains and the Snake River Plain show a consistent pattern of negative site response (i.e. deamplification), while areas with a higher degree of sediments, such as the grabens of the Basin and Range, show positive site response (i.e. amplification). Finally, site responses were found to vary with frequency, becoming less variable and more pronounced as frequency increases.

Rayleigh Wave Tomography of Mid-Continent Rift (MCR) using Earthquake and Ambient Noise Data

NASA Astrophysics Data System (ADS)

Aleqabi, G. I.; Wiens, D.; Wysession, M. E.; Shen, W.; van der Lee, S.; Revenaugh, J.; Frederiksen, A. W.; Darbyshire, F. A.; Stein, S. A.; Jurdy, D. M.; Wolin, E.; Bollmann, T. A.

2015-12-01

The structure of the North American Mid-Continent Rift Zone (MCRZ) is examined using Rayleigh waves from teleseismic earthquakes and ambient seismic noise recorded by the Superior Province Rifting EarthScope Experiment (SPREE). Eighty-four broadband seismometers were deployed during 2011-2013 in Minnesota and Wisconsin, USA, and Ontario, CA, along three lines; two across the rift axis and the third along the rift axis. These stations, together with the EarthScope Transportable Array, provided excellent coverage of the MCRZ. The 1.1 Ga Mesoproterozoic failed rift consists of two arms, buried under post-rifting sedimentary formations that meet at Lake Superior. We compare two array-based tomography methods using teleseismic fundamental mode Rayleigh waves phase and amplitude measurements: the two-plane wave method (TPWM, Forsyth, 1998) and the automated surface wave phase velocity measuring system (ASWMS, Jin and Gaherty, 2015). Both array methods and the ambient noise method give relatively similar results showing low velocity zones extending along the MCRZ arms. The teleseismic Rayleigh wave results from 18 - 180 s period are combined with short period phase velocity results (period 8-30 s) obtained from ambient noise by cross correlation. Phase velocities from the methods are very similar at periods of 18-30 where results overlap; in this period range we use the average of the noise and teleseismic results. Finally the combined phase velocity curve is inverted using a Monte-Carlo inversion method at each geographic point in the model. The results show low velocities at shallow depths (5-10 km) that are the result of very deep sedimentary fill within the MCRZ. Deeper-seated low velocity regions may correspond to mafic underplating of the rift zone.

Engaging students in geodesy: A quantitative InSAR module for undergraduate tectonics and geophysics classes

NASA Astrophysics Data System (ADS)

Taylor, H.; Charlevoix, D. J.; Pritchard, M. E.; Lohman, R. B.

2013-12-01

In the last several decades, advances in geodetic technology have allowed us to significantly expand our knowledge of processes acting on and beneath the Earth's surface. Many of these advances have come as a result of EarthScope, a community of scientists conducting multidisciplinary Earth science research utilizing freely accessible data from a variety of instruments. The geodetic component of EarthScope includes the acquisition of synthetic aperture radar (SAR) images, which are archived at the UNAVCO facility. Interferometric SAR complements the spatial and temporal coverage of GPS and allows monitoring of ground deformation in remote areas worldwide. However, because of the complex software required for processing, InSAR data are not readily accessible to most students. Even with these challenges, exposure at the undergraduate level is important for showing how geodesy can be applied in various areas of the geosciences and for promoting geodesy as a future career path. Here we present a module focused on exploring the tectonics of the western United States using InSAR data for use in undergraduate tectonics and geophysics classes. The module has two major objectives: address topics concerning tectonics in the western U.S. including Basin and Range extension, Yellowstone hotspot activity, and creep in southern California, and familiarize students with how imperfect real-world data can be manipulated and interpreted. Module questions promote critical thinking skills and data literacy by prompting students to use the information given to confront and question assumptions (e.g. 'Is there a consistency between seismic rates and permanent earthquake deformation? What other factors might need to be considered besides seismicity?'). The module consists of an introduction to the basics of InSAR and three student exercises, each focused on one of the topics listed above. Students analyze pre-processed InSAR data using MATLAB, or an Excel equivalent, and draw on GPS and creepmeter datasets for comparison. Exercises were developed following Backward Design and initial feedback was provided by curriculum experts and several undergraduate students. Evaluation of the impact of the module on student understanding of InSAR will be conducted in the fall with volunteers from tectonics and geophysics classes. Students will be given pre- and post-module surveys to evaluate overall effectiveness and areas for improvement. This module will be disseminated on the UNAVCO website after finalization.

Slab-plume interaction beneath the Pacific Northwest

NASA Astrophysics Data System (ADS)

Obrebski, Mathias; Allen, Richard M.; Xue, Mei; Hung, Shu-Huei

2010-07-01

The Pacific Northwest has undergone complex plate reorganization and intense tectono-volcanic activity to the east during the Cenozoic (last 65 Ma). Here we show new high-resolution tomographic images obtained using shear and compressional data from the ongoing USArray deployment that demonstrate first that there is a continuous, whole-mantle plume beneath the Yellowstone Snake River Plain (YSRP) and second, that the subducting Juan de Fuca (JdF) slab is fragmented and even absent beneath Oregon. The analysis of the geometry of our tomographic models suggests that the arrival and emplacement of the large Yellowstone plume had a substantial impact on the nearby Cascadia subduction zone, promoting the tearing and weakening of the JdF slab. This interpretation also explains several intriguing geophysical properties of the Cascadia trench that contrast with most other subduction zones, such as the absence of deep seismicity and the trench-normal fast direction of mantle anisotropy. The DNA velocity models are available for download and slicing at http://dna.berkeley.edu.

3-D Upper-Mantle Shear Velocity Model Beneath the Contiguous United States Based on Broadband Surface Wave from Ambient Seismic Noise

NASA Astrophysics Data System (ADS)

Xie, Jun; Chu, Risheng; Yang, Yingjie

2018-05-01

Ambient noise seismic tomography has been widely used to study crustal and upper-mantle shear velocity structures. Most studies, however, concentrate on short period (< 50 s) surface wave from ambient noise, while studies using long period surface wave from ambient noise are limited. In this paper, we demonstrate the feasibility of using long-period surface wave from ambient noise to study the lithospheric structure on a continental scale. We use broadband Rayleigh wave phase velocities to obtain a 3-D V S structures beneath the contiguous United States at period band of 10-150 s. During the inversion, 1-D shear wave velocity profile is parameterized using B-spline at each grid point and is inverted with nonlinear Markov Chain Monte Carlo method. Then, a 3-D shear velocity model is constructed by assembling all the 1-D shear velocity profiles. Our model is overall consistent with existing models which are based on multiple datasets or data from earthquakes. Our model along with the other post-USArray models reveal lithosphere structures in the upper mantle, which are consistent with the geological tectonic background (e.g., the craton root and regional upwelling provinces). The model has comparable resolution on lithosphere structures compared with many published results and can be used for future detailed regional or continental studies and analysis.

Unveiling the lithospheric structure of the US Interior using the USArray Transportable Array

NASA Astrophysics Data System (ADS)

Moschetti, M. P.; Ritzwoller, M. H.; Lin, F.; Shen, W.; Yang, Y.

2009-12-01

We present current results from ambient noise tomography (ANT) and earthquake surface wave tomography applied to the USARRAY Transportable Array (TA) for the western and central US. We have processed ambient seismic noise data since October 2004 to produce cumulative Rayleigh and Love wave dispersion maps (from about 6 to 40 sec period) within the footprint of the TA. The high spatial density of these instruments results in dispersion maps with a resolution of about the average inter-station distance (70 km) and far exceeds previous surface wave tomographic results for the US interior. The dispersion maps from ANT are complemented by Rayleigh wave phase speed maps from teleseismic earthquake tomography (25 - 100 sec period). The development of a new method of surface wave tomography, termed Eikonal tomography, that models wavefront complexity and off great-circle propagation allows for the robust estimation of phase velocity azimuthal anisotropy. Eikonal tomography has been applied to ambient seismic noise and earthquake measurements and provides a means to compare and vet results in the period band of overlap (25 - 40 sec). In addition, the recent application of this method to Love waves from teleseismic earthquakes provides dispersion measurements up to 50 sec period. These longer period Love wave dispersion measurements may improve the characterization of anisotropy in the uppermost mantle. In addition to the current dispersion maps, we present regional-scale 3-D models of isotropic and anisotropic shear-velocities for the crust and uppermost mantle beneath the western US. Because dispersion measurements from ambient seismic noise include short period (<20 sec) information, they provide a strong constraint on the shear-velocity structure of the crust and uppermost mantle. A radially anisotropic shear-velocity model of the crust and uppermost mantle is constructed by simultaneously inverting Rayleigh and Love wave dispersion measurements from ANT and from earthquake tomography. Models with isotropic and radially anisotropic mantle shear-velocities do not fit the Rayleigh and Love wave measurements simultaneously across large regions of the western US, and the models present a Rayleigh-Love misfit discrepancy at the periods most sensitive to crustal velocity structures. However, by introducing positive radial anisotropy (Vsh>Vsv) to the middle and lower crust, this misfit discrepancy is resolved. Higher amplitude crustal radial anisotropy is observed in the predominant extensional provinces of the western US and is thought to result from the alignment of anisotropic crustal minerals during extension and deformation. Several regions of the western US remain poorly fit by the 3-D radially anisotropic shear-velocity model. These include the Olympic Peninsula, Mendocino Triple Junction, southern Cascadia backarc, Yakima Fold Belt, Wasatch Front, Salton Trough and Great Valley. We investigate various additional model parametrizations and the effect of breaking the constraint on the monotonic increase of crustal velocities with depth to resolve crustal shear-velocity structure in these regions. These techniques will readily be applied to data from the US Interior as the TA moves to the east.

A Preliminary Teleseismic Investigation of the Crust and Mantle Lithosphere Obtained from BISN in the Western Canadian Arctic

NASA Astrophysics Data System (ADS)

Schaeffer, A. J.; Snyder, D. B.; Cairns, S.; Elliot, B.; Audet, P.; Esteve, C.; Murray-Bergquist, L.; Falck, H.

2016-12-01

The tectonic evolution of the Beaufort Sea continental margin has contributed to the maturation of these rocks into a major petroleum reservoir. Recent shallow offshore seismic reflection data suggest that Banks Island represents thin crust along a rifted margin established during the opening of the Arctic Ocean. In this case, rifting of the margin caused Banks Island to subside and accumulate sediments rich in petroleum source material. The cooling history and further subsidence of these sediments is important for understanding the thermal maturation of petroleum products. Recently published surface-wave velocity models of North America indicate seismic velocities at 100-150 km depths similar to those beneath Canada's diamond mines in the central Slave craton north of Yellowknife. These results imply that Banks Island is part of the Canadian Shield and that any kimberlites found thereon might contain diamonds. However, the fast velocities are inconsistent with this being a tectonically disrupted and thinned lithosphere along the Arctic margin of the Canada Basin. The problem is therefore to reconcile mantle structure typical of the Canadian Shield with crust typical of a rifted passive margin. Possibly related seismicity beneath the Mackenize River Delta and offshore in the Beaufort Sea has been observed for decades but its origin remains unknown, although has been suggested as due to incipient subduction of oceanic lithosphere beneath the North American craton. Resolving these questions requires high-resolution 3-D seismic models obtained from an array of broadband seismograph stations. Here we present preliminary results on the structure of the crust and uppermost mantle underlying the western Canadian Arctic. These results are generated using new data from the Banks Island Seismograph Network (BISN), three stations installed over the summer of 2014 and 2015; augmented with several USArray Transportable Array stations and older POLARIS and CNSN stations on neighbouring Arctic Islands.

Macro-scale Tectonics of the Eastern North American Shield: Insights from a new Absolute P-wave Tomographic Model for North America.

NASA Astrophysics Data System (ADS)

Boyce, A.; Bastow, I. D.; Golos, E. M.; Burdick, S.; van der Hilst, R. D.; Rondenay, S.

2017-12-01

The Grenville orogen is a 1Ga old, 4000km long tectonic collision zone that bounds the North American Shield to the east, often drawing comparisons to the modern-day Himalayas in collisional style and extent. Local studies of the Grenville province are legion, however it remains enigmatic at the macro scale due to its large spatial footprint (from Labrador to Mexico), interaction with Phanerozoic tectonics and present-day sedimentary cover. Recently, the USArray Transportable Array seismic stations have gone someway to addressing this issue but station coverage remains sparse in global absolute wavespeed models in the shield regions further north. However, the newly published method of Boyce et. al., (2017) enables data from regional seismic networks to be incorporated into these global models. Here we use this method to add 13000 new P-wave arrivals from stations in Canada to the continental portion of the global absolute wavespeed tomographic model of Burdick et. al., (2017). Thus we are able to seismically illuminate, for the first time, mantle seismic structure for the entire footprint of the Grenville Orogen. Recent work suggests that in SE Canada the edge of the Superior craton has undergone post formation modification. Using these images it will be possible to investigate whether craton edge modification is ubiquitous along the entire Grenville front and whether oblique or direct "head-on" shortening was dominant during the collision of Laurentia and Amazonia at 1Ga. Through further comparison with the GLimER 2D receiver function profiles (Rondenay et. al., 2017), we aim to unify theories from local scale studies for evolution of the eastern portion of stable North America. Furthermore, we will be able to constrain the morphology of the North American keel and assess to what extent this may influence present day asthenospheric flow fields and the resulting implications for modification of the cratonic root.

Imaging paleoslabs in the D″ layer beneath Central America and the Caribbean using seismic waveform inversion

PubMed Central

Borgeaud, Anselme F. E.; Kawai, Kenji; Konishi, Kensuke; Geller, Robert J.

2017-01-01

D″ (Dee double prime), the lowermost layer of the Earth’s mantle, is the thermal boundary layer (TBL) of mantle convection immediately above the Earth’s liquid outer core. As the origin of upwelling of hot material and the destination of paleoslabs (downwelling cold slab remnants), D″ plays a major role in the Earth’s evolution. D″ beneath Central America and the Caribbean is of particular geodynamical interest, because the paleo- and present Pacific plates have been subducting beneath the western margin of Pangaea since ~250 million years ago, which implies that paleoslabs could have reached the lowermost mantle. We conduct waveform inversion using a data set of ~7700 transverse component records to infer the detailed three-dimensional S-velocity structure in the lowermost 400 km of the mantle in the study region so that we can investigate how cold paleoslabs interact with the hot TBL above the core-mantle boundary (CMB). We can obtain high-resolution images because the lowermost mantle here is densely sampled by seismic waves due to the full deployment of the USArray broadband seismic stations during 2004–2015. We find two distinct strong high-velocity anomalies, which we interpret as paleoslabs, just above the CMB beneath Central America and Venezuela, respectively, surrounded by low-velocity regions. Strong low-velocity anomalies concentrated in the lowermost 100 km of the mantle suggest the existence of chemically distinct denser material connected to low-velocity anomalies in the lower mantle inferred by previous studies, suggesting that plate tectonics on the Earth’s surface might control the modality of convection in the lower mantle. PMID:29209659

A California statewide three-dimensional seismic velocity model from both absolute and differential times

USGS Publications Warehouse

Lin, G.; Thurber, C.H.; Zhang, H.; Hauksson, E.; Shearer, P.M.; Waldhauser, F.; Brocher, T.M.; Hardebeck, J.

2010-01-01

We obtain a seismic velocity model of the California crust and uppermost mantle using a regional-scale double-difference tomography algorithm. We begin by using absolute arrival-time picks to solve for a coarse three-dimensional (3D) P velocity (VP) model with a uniform 30 km horizontal node spacing, which we then use as the starting model for a finer-scale inversion using double-difference tomography applied to absolute and differential pick times. For computational reasons, we split the state into 5 subregions with a grid spacing of 10 to 20 km and assemble our final statewide VP model by stitching together these local models. We also solve for a statewide S-wave model using S picks from both the Southern California Seismic Network and USArray, assuming a starting model based on the VP results and a VP=VS ratio of 1.732. Our new model has improved areal coverage compared with previous models, extending 570 km in the SW-NE directionand 1320 km in the NW-SE direction. It also extends to greater depth due to the inclusion of substantial data at large epicentral distances. Our VP model generally agrees with previous separate regional models for northern and southern California, but we also observe some new features, such as high-velocity anomalies at shallow depths in the Klamath Mountains and Mount Shasta area, somewhat slow velocities in the northern Coast Ranges, and slow anomalies beneath the Sierra Nevada at midcrustal and greater depths. This model can be applied to a variety of regional-scale studies in California, such as developing a unified statewide earthquake location catalog and performing regional waveform modeling.

Clustering P-Wave Receiver Functions To Constrain Subsurface Seismic Structure

NASA Astrophysics Data System (ADS)

Chai, C.; Larmat, C. S.; Maceira, M.; Ammon, C. J.; He, R.; Zhang, H.

2017-12-01

The acquisition of high-quality data from permanent and temporary dense seismic networks provides the opportunity to apply statistical and machine learning techniques to a broad range of geophysical observations. Lekic and Romanowicz (2011) used clustering analysis on tomographic velocity models of the western United States to perform tectonic regionalization and the velocity-profile clusters agree well with known geomorphic provinces. A complementary and somewhat less restrictive approach is to apply cluster analysis directly to geophysical observations. In this presentation, we apply clustering analysis to teleseismic P-wave receiver functions (RFs) continuing efforts of Larmat et al. (2015) and Maceira et al. (2015). These earlier studies validated the approach with surface waves and stacked EARS RFs from the USArray stations. In this study, we experiment with both the K-means and hierarchical clustering algorithms. We also test different distance metrics defined in the vector space of RFs following Lekic and Romanowicz (2011). We cluster data from two distinct data sets. The first, corresponding to the western US, was by smoothing/interpolation of receiver-function wavefield (Chai et al. 2015). Spatial coherence and agreement with geologic region increase with this simpler, spatially smoothed set of observations. The second data set is composed of RFs for more than 800 stations of the China Digital Seismic Network (CSN). Preliminary results show a first order agreement between clusters and tectonic region and each region cluster includes a distinct Ps arrival, which probably reflects differences in crustal thickness. Regionalization remains an important step to characterize a model prior to application of full waveform and/or stochastic imaging techniques because of the computational expense of these types of studies. Machine learning techniques can provide valuable information that can be used to design and characterize formal geophysical inversion, providing information on spatial variability in the subsurface geology.

Focusing the EarthScope for a Broader Audience

NASA Astrophysics Data System (ADS)

Smith-Konter, B. R.

2011-12-01

One of the most challenging milestones of scientific research is often the translation of a technical result into a clear "teachable moment" that is accessible (and interesting!) to a broader audience. The success of this milestone can largely be measured by its effectiveness to inspire interest and enthusiasm in the non-scientist. Moreover, as 4D multimedia now dominates most aspects of our social environment, science "teaching" now also requires intervention of visualization technology and animation to portray research results in an inviting and stimulating manner. In response to these needs, a primary objective of the EarthScope Education and Outreach program is to transform technical science into teachable products for a technologically thriving generation. Following the Incorporated Research Institutions for Seismology (IRIS)'s lead in developing interactive Earth science kiosk multimedia (bundled in a free product called Active Earth), a major focus of this EarthScope CAREER project is aimed at the construction and installation of customized EarthScope-themed touch screen kiosks in local communities. These kiosks are helping to educate a broader audience about EarthScope's unique instrumentation and observations using interactive animations, games, and virtual field trips. An additional focus of this CAREER project is aimed at the development of several Earthquakes in Action teaching modules for grades 6-12, which have been successfully tested and implemented in both teacher-prep courses and an annual high school summer geosciences camp at the University of Texas at El Paso. These activities are beginning to shape a new pathway for how teachers teach and students learn about planet Earth and its fantastic EarthScope - one click (and touch) at a time.

The Yellowstone ‘hot spot’ track results from migrating Basin Range extension

USGS Publications Warehouse

Foulger, Gillian R.; Christiansen, Robert L.; Anderson, Don L.; Foulger, Gillian R.; Lustrino, Michele; King, Scott D.

2015-01-01

Whether the volcanism of the Columbia River Plateau, eastern Snake River Plain, and Yellowstone (western U.S.) is related to a mantle plume or to plate tectonic processes is a long-standing controversy. There are many geological mismatches with the basic plume model as well as logical flaws, such as citing data postulated to require a deep-mantle origin in support of an “upper-mantle plume” model. USArray has recently yielded abundant new seismological results, but despite this, seismic analyses have still not resolved the disparity of opinion. This suggests that seismology may be unable to resolve the plume question for Yellowstone, and perhaps elsewhere. USArray data have inspired many new models that relate western U.S. volcanism to shallow mantle convection associated with subduction zone processes. Many of these models assume that the principal requirement for surface volcanism is melt in the mantle and that the lithosphere is essentially passive. In this paper we propose a pure plate model in which melt is commonplace in the mantle, and its inherent buoyancy is not what causes surface eruptions. Instead, it is extension of the lithosphere that permits melt to escape to the surface and eruptions to occur—the mere presence of underlying melt is not a sufficient condition. The time-progressive chain of rhyolitic calderas in the eastern Snake River Plain–Yellowstone zone that has formed since basin-range extension began at ca. 17 Ma results from laterally migrating lithospheric extension and thinning that has permitted basaltic magma to rise from the upper mantle and melt the lower crust. We propose that this migration formed part of the systematic eastward migration of the axis of most intense basin-range extension. The bimodal rhyolite-basalt volcanism followed migration of the locus of most rapid extension, not vice versa. This model does not depend on seismology to test it but instead on surface geological observations.

USArray Receiver Function Imaging of Multiple-Layer Crustal Structure of the Contiguous United States

NASA Astrophysics Data System (ADS)

Ma, X.; Lowry, A. R.; Ravat, D.

2014-12-01

Thickness andseismic velocity of crustal layers are useful for understanding the history and evolution of continental lithosphere. Lowry and Pérez-Gussinyé (2011) observed that low bulk crustal seismic velocity ratio, Vp/Vs, strongly correlates with high geothermal gradient and active deformation, indicating quartz (to which Vp/Vs is most sensitive) plays a role in these processes. The lower crust (where ductile flow occurs which might explain the relationship) is commonly thought to be quartz-poor. However, layering of the crust may represent changes in either lithology or the phase of quartz. Laboratory strain-stress experiments on quartz indicate that near the a- to b-quartz phase transition, both Vp and Vp/Vs initially drop dramatically but then increase relative to the a-quartz regime because Young's modulus initially decreases by 30% before increasing by a net ~20%. Shear modulus varies only ~3% across the transition. Crustal structure is commonly represented by an upper, mid- and lower layer (e.g., Crust1.0) and conceptualized as primarily reflecting a change to more mafic lithology at greater depth, but estimates of Moho temperature indicate a quartz phase transition should be present in much of the western and central U.S. We have imaged multiple layering of the contiguous U.S. by applying a new cross-correlation and stacking method to USArray receiver functions. Synthetic models of a multiple layer crust indicate 'splitting' of converted-phase arrivals would be expected if a quartz phase transition were responsible. Preliminary imaging using cross-correlation of observed receiver functions with multiple layer synthetics demonstrates a marked improvement in correlation coefficients relative to a single-layer crust. In this presentation we will examine observational evidence for possible a- to b- phase transition layering (indicating quartz at depth) and compare with depths predicted for the quartz phase transition based on Pn-derived Moho temperatures and estimates of magnetic Curie depths.

Controls on Magmatic and Hydrothermal Processes at Yellowstone Supervolcano: The Wideband Magnetotelluric Component of an Integrated MT/Seismic Investigation

NASA Astrophysics Data System (ADS)

Schultz, A.; Bennington, N. L.; Bowles-martinez, E.; Imamura, N.; Cronin, R. A.; Miller, D. J.; Hart, L.; Gurrola, R. M.; Neal, B. A.; Scholz, K.; Fry, B.; Carbonari, R.

2017-12-01

Previous seismic and magnetotelluric (MT) studies beneath Yellowstone (YS) have provided insight into the origin and migration of magmatic fluids within the volcanic system. However, important questions remain concerning the generation of magmatism at YS, the migration and storage of these magmatic fluids, as well as their relationships to hydrothermal expressions. Analysis of regional-scale EarthScope MT data collected previously suggests a relative absence of continuity in crustal partial melt accumulations directly beneath YS. This is in contrast to some seismic interpretations, although such long-period MT data have limited resolving power in the upper-to-mid crustal section. A wideband MT experiment was designed as a component of an integrated MT/seismic project to examine: the origin and location of magmatic fluids at upper mantle/lower crustal depths, the preferred path of migration for these magmatic fluids into the mid- to upper-crust, the resulting distribution of the magma reservoir, the composition of the magma reservoir, and implications for future volcanism at YS. A high-resolution wideband MT survey was carried out in the YS region in the summer of 2017, with more than forty-five wideband stations installed within and immediately surrounding the YS National Park boundary. These data provided nearly six decades of bandwidth ( 10-3 Hz -to- 103 Hz). Extraordinary permitting restrictions prevented us from using conventional installation methods at many of our sites, and an innovative "no-dig" subaerial method of wideband MT was developed and used successfully. Using these new data along with existing MT datasets, we are inverting for the 3D resistivity structure at upper crustal through upper mantle scales at YS. Complementary to this MT work, a joint inversion for the 3D crustal velocity structure is being carried out using both ambient noise and earthquake travel time data. Taken together, these data should better constrain the crustal velocity structure of this volcanic system and produce enhanced images of magma storage.

Seismic anisotropy in the upper mantle beneath the MAGIC array, mid-Atlantic Appalachians: Constraints from SKS splitting and quasi-Love wave propagation

NASA Astrophysics Data System (ADS)

Aragon, J. C.; Long, M. D.; Benoit, M. H.; Servali, A.

2016-12-01

North America's eastern passive continental margin has been modified by several cycles of supercontinent assembly. Its complex surface geology and distinct topography provide evidence of these events, while also raising questions about the extent of deformation in the continental crust, lithosphere, and mantle during past episodes of rifting and mountain building. The Mid-Atlantic Geophysical Integrative Collaboration (MAGIC) is an EarthScope and GeoPRISMS-funded project that involves a collaborative effort among seismologists, geodynamicists, and geomorphologists. One component of the project is a broadband seismic array consisting of 28 instruments in a linear path from coastal Virginia to western Ohio, which operated between October 2013 and October 2016. A key science question addressed by the MAGIC project is the geometry of past lithospheric deformation and present-day mantle flow beneath the Appalachians, which can be probed using observations of seismic anisotropy Here we present observations of SKS splitting and quasi-Love wave arrivals from stations of the MAGIC array, which together constrain seismic anisotropy in the upper mantle. SKS splitting along the array reveals distinct regions of upper mantle anisotropy, with stations in and to the west of the range exhibiting fast directions parallel to the strike of the mountains. In contrast, weak splitting and null SKS arrivals dominate eastern stations in the coastal plain. Documented Love-to-Rayleigh wave scattering for surface waves originating the magnitude 8.3 Illapel, Chile earthquakes in September 2015 provides complementary constraints on anisotropy. These quasi-Love wave arrivals suggest a pronounced change in upper mantle anisotropy at the eastern edge of present-day Appalachian topography. Together, these observations increase our understanding of the extent of lithospheric deformation beneath North America associated with Appalachian orogenesis, as well as the pattern of present-day mantle flow beneath the passive margin.

Cascadia Initiative Reveals Accumulation of Buoyant Material Beneath the Subducting Juan de Fuca Plate

NASA Astrophysics Data System (ADS)

Hawley, W. B.; Allen, R. M.; Richards, M. A.

2015-12-01

The Cascadia Initiative is a four-year (2011-2015) amphibious seismic deployment that covers the Juan de Fuca plate and the Cascadia Subduction Zone. It is comprised of 70 broadband ocean-bottom seismometers that occupy 120 sites in total, as well as 27 land-based stations. This array offers a unique opportunity to study the 3D structure of a subduction zone in unprecedented detail. We present the results of an inversion using teleseismic body waves recorded by the Cascadia Initiative, EarthScope, and other regional and temporary networks in the Pacific Northwest. A low-velocity feature is visible beneath the subducting slab at shallow depths. Previous studies report ponding of low-viscosity, buoyant material at the top of the asthenosphere, unable to rise through the impermeable lithospheric lid. We show that as the lithospheric lid descends into the mantle, this material is not advected with it; rather, due to its own weakness and buoyancy, it accumulates at the subduction zone. Such material could be partly responsible for the rapid uplift and volcanism in the Coast Range of California, in the wake of the northward migration of the Mendocino Triple Junction. This newly observed feature may play an important role in the structure of subduction zones, but understanding the extent of that role on a global scale will require amphibious seismic deployments in other subduction zones.

The PBO Nucleus: Integration of the Existing Continuous GPS Networks in the Western U.S.

NASA Astrophysics Data System (ADS)

Blume, F.; Anderson, G.; Freymueller, J. T.; Herring, T. A.; Melbourne, T. I.; Murray, M. H.; Prescott, W. H.; Smith, R. B.; Wernicke, B.

2004-12-01

Tectonic and earthquake research in the US has experienced a quiet revolution over the last decade precipitated by the recognition that slow-motion faulting events can both trigger and be triggered by regular earthquakes. Transient motion has now been found in essentially all tectonic environments, and the detection and analysis of such events is the first-order science target of the EarthScope Project. Because of this and a host of other fundamental tectonics questions that can be answered only with long-duration geodetic time series, the incipient 1400-station EarthScope Plate Boundary Observatory (PBO) network has been designed to leverage 432 existing continuous GPS stations whose measurements extend back over a decade. The irreplaceable recording history of these stations will accelerate EarthScope scientific return by providing the highest possible resolution. This resolution will be used to detect and understand transients, to determine the three-dimensional velocity field (particularly vertical motion), and to improve measurement precision by understanding the complex noise sources inherent in GPS. The PBO Nucleus Project is designed operate, maintain and upgrade a subset of six western U.S. geodetic networks: the Alaska Deformation Array (AKDA), Bay Area Regional Deformation network (BARD), the Basin and Range Geodetic Network (BARGEN), the Eastern Basin and Range/Yellowstone network (EBRY), the Pacific Northwest Geodetic Array (PANGA), and the Southern California Integrated Geodetic Network (SCIGN), until they are subsumed by PBO in 2008. Uninterrupted data flow from these stations will effectively double the time-series length of PBO over the expected life of EarthScope, and create, for the first time, a single GPS-based geodetic network in the US. Other existing sites will remain in operation under support from non-NSF sources (e.g. the USGS), and EarthScope will benefit from their continued operation. On the grounds of relevance to EarthScope science goals, geographic distribution and data quality, 209 of the 432 existing stations have been selected as the nucleus upon which to build PBO. We have begun converting these stations to a PBO-compatible mode of operation; data now flow directly to PBO archives and processing centers while maintenance, operations, and meta-data requirements are currently under upgrade to PBO standards.

Seismic rate changes associated with seasonal, annual, and decadal changes in the cryosphere

NASA Astrophysics Data System (ADS)

Sauber, J. M.; Luthcke, S. B.; Hall, D. K.

2012-12-01

Near the Bering Glacier Global Fiducial Program (GFP) in southern Alaska large cryospheric fluctuations occur in a region of upper crustal faulting and folding associated with collision and accretion of the Yakutat terrane. In this study we report constraints on seasonal, annual and decadal cryospheric changes estimated over the last decade from field, aircraft and satellite measurements and we evaluate the influence of cryospheric changes on the background seismic rate. Multi-year images from the Bering Glacier GFP are available since mid-2003 to constrain changes in extent of the Bering Glacier and to discern feature changes in the glacial surface. Starting around the same time, satellite gravimetric measurements from the Gravity Recovery and Climate experiment (GRACE) commenced. Large spatial-scale mass change calculated from the GRACE mascon solution of Luthcke et al. [2012] indicate a general trend of annual ice mass loss for southern Alaska but with large, variable seasonal mass fluctuations. Since 2007 the station position of a continuous GPS site near Cape Yakataga (Alaska EarthScope PBO site, AB35) has been available as well. In addition to changes in the geodetic position due to tectonic motion, this GPS station shows large seasonal excursions in the detrended vertical and horizontal position components consistent with snow loading in the fall and winter and melt onset/mass decrease in the spring/summer. To better understand the timing of processes responsible for the onset of cryospheric mass loss documented in the GRACE data, we examined changes in the snow cover extent and the onset of melt in the spring. We calculated the elastic displacements of the solid Earth and theoretical earthquake failure criteria associated with these annual and seasonal ice and snow changes. Additionally, we compared the seismic rate (M>1.8) from a reference background time period against other time periods with variable ice or tectonic change characteristics to test the significance of seismic rate changes. Our earlier results suggest statistically significant changes in the background seismic rate associated with large seasonal mass changes.

Seismic Rate Changes Associated with Seasonal, Annual, and Decadal Changes in the Cryosphere

NASA Technical Reports Server (NTRS)

Sauber-Rosenberg, Jeanne

2012-01-01

Near the Bering Glacier Global Fiducial site in southern Alaska large cryospheric fluctuations occur in a region of upper crustal faulting and folding associated with collision and accretion of the Yakutat terrane. In this study we report constraints on seasonal, annual and decadal cryospheric changes estimated over the last decade from field, aircraft and satellite measurements, and we evaluate the influence of cryospheric changes on the background seismic rate. Multi-year images from the Bering Glacier global fiducial site are available since mid-2003 to constrain changes in extent of the Bering Glacier and to discern feature changes in the glacial surface. Starting around the same time, satellite gravimetric measurements from the Gravity Recovery and Climate experiment (GRACE) commenced. Large spatial-scale mass change calculated from the GRACE 1deg x 1deg mascon solution of Luthcke et al. [2012] indicate a general trend of annual ice mass loss for southern Alaska but with large, variable seasonal mass fluctuations. Since 2007, the station position of a continuous GPS site near Cape Yakataga (Alaska EarthScope PBO site, AB35) has been available as well. In addition to changes in the geodetic position due to tectonic motion, this GPS station shows large seasonal excursions in the detrended vertical and horizontal position components consistent with snow loading in the fall and winter and melt onset/mass decrease in the spring/summer. To better understand the timing of processes responsible for the onset of cryospheric mass loss documented in the GRACE data, we examined changes in the snow cover extent and the onset of melt in the spring. We calculated the surface displacements of the solid Earth and theoretical earthquake failure criteria associated with these annual and seasonal ice and snow changes using layered elastic half-space. Additionally, we compared the seismic rate (M>1.8) from a reference background time period against other time periods with variable ice or tectonic change characteristics to test the significance of seismic rate changes. Our earlier results suggest statistically significant changes in the background seismic rate associated with large seasonal mass changes. INDEX

EMERALD: A Flexible Framework for Managing Seismic Data

NASA Astrophysics Data System (ADS)

West, J. D.; Fouch, M. J.; Arrowsmith, R.

2010-12-01

The seismological community is challenged by the vast quantity of new broadband seismic data provided by large-scale seismic arrays such as EarthScope’s USArray. While this bonanza of new data enables transformative scientific studies of the Earth’s interior, it also illuminates limitations in the methods used to prepare and preprocess those data. At a recent seismic data processing focus group workshop, many participants expressed the need for better systems to minimize the time and tedium spent on data preparation in order to increase the efficiency of scientific research. Another challenge related to data from all large-scale transportable seismic experiments is that there currently exists no system for discovering and tracking changes in station metadata. This critical information, such as station location, sensor orientation, instrument response, and clock timing data, may change over the life of an experiment and/or be subject to post-experiment correction. Yet nearly all researchers utilize metadata acquired with the downloaded data, even though subsequent metadata updates might alter or invalidate results produced with older metadata. A third long-standing issue for the seismic community is the lack of easily exchangeable seismic processing codes. This problem stems directly from the storage of seismic data as individual time series files, and the history of each researcher developing his or her preferred data file naming convention and directory organization. Because most processing codes rely on the underlying data organization structure, such codes are not easily exchanged between investigators. To address these issues, we are developing EMERALD (Explore, Manage, Edit, Reduce, & Analyze Large Datasets). The goal of the EMERALD project is to provide seismic researchers with a unified, user-friendly, extensible system for managing seismic event data, thereby increasing the efficiency of scientific enquiry. EMERALD stores seismic data and metadata in a state-of-the-art open source relational database (PostgreSQL), and can, on a timed basis or on demand, download the most recent metadata, compare it with previously acquired values, and alert the user to changes. The backend relational database is capable of easily storing and managing many millions of records. The extensible, plug-in architecture of the EMERALD system allows any researcher to contribute new visualization and processing methods written in any of 12 programming languages, and a central Internet-enabled repository for such methods provides users with the opportunity to download, use, and modify new processing methods on demand. EMERALD includes data acquisition tools allowing direct importation of seismic data, and also imports data from a number of existing seismic file formats. Pre-processed clean sets of data can be exported as standard sac files with user-defined file naming and directory organization, for use with existing processing codes. The EMERALD system incorporates existing acquisition and processing tools, including SOD, TauP, GMT, and FISSURES/DHI, making much of the functionality of those tools available in a unified system with a user-friendly web browser interface. EMERALD is now in beta test. See emerald.asu.edu or contact john.d.west@asu.edu for more details.

Seismic Anisotropy Beneath the Eastern Flank of the Rio Grande Rift

NASA Astrophysics Data System (ADS)

Benton, N. W.; Pulliam, J.

2015-12-01

Shear wave splitting was measured across the eastern flank of the Rio Grande Rift (RGR) to investigate mechanisms of upper mantle anisotropy. Earthquakes recorded at epicentral distances of 90°-130° from EarthScope Transportable Array (TA) and SIEDCAR (SC) broadband seismic stations were examined comprehensively, via the Matlab program "Splitlab", to determine whether SKS and SKKS phases indicated anisotropic properties. Splitlab allows waveforms to be rotated, filtered, and windowed interactively and splitting measurements are made on a user-specified waveform segment via three independent methods simultaneously. To improve signal-to-noise and improve reliability, we stacked the error surfaces that resulted from grid searches in the measurements for each station location. Fast polarization directions near the Rio Grande Rift tend to be sub-parallel to the RGR but then change to angles that are consistent with North America's average plate motion, to the east. The surface erosional depression of the Pecos Valley coincides with fast polarization directions that are aligned in a more northerly direction than their neighbors, whereas the topographic high to the east coincides with an easterly change of the fast axis.The area above a mantle high velocity anomaly discovered separately via seismic tomography which may indicate thickened lithosphere, corresponds to unusually large delay times and fast polarization directions that are more closely aligned to a north-south orientation. The area of southeastern New Mexico that falls between the mantle fast anomaly and the Great Plains craton displays dramatically smaller delay times, as well as changes in fast axis directions toward the northeast. Changes in fast axis directions may indicate flow around the mantle anomaly; small delay times could indicate vertical or attenuated flow.

Seismic evidence for the depression of the D″ discontinuity beneath the Caribbean: Implication for slab heating from the Earth's core

NASA Astrophysics Data System (ADS)

Ko, Justin Yen-Ting; Hung, Shu-Huei; Kuo, Ban-Yuan; Zhao, Li

2017-06-01

The lowermost 100-300 km of the Earth's mantle commonly regarded as the thermal boundary layer (TBL) of mantle circulation is characterized by its complex physical properties. Beneath the Caribbean this so-called D″ layer features relatively high velocities and abrupt impedance increase at the top (designated as the D″ discontinuity). These seismic characteristics have been attributed to the accumulation of ancient subducted slab material and the phase transition in the major lower mantle mineral of pervoskite. Geodynamic models predict that the blanketing cold slabs may trap enough heat from core to be buoyantly destabilized, and eventually broken apart and entrained into the bottom of the convection cell. Here we explore the D″ structure with unprecedented resolution through modeling traveltimes, amplitudes, and waveform shapes from the USArray. We find an east-to-west asymmetrical undulation of the D″ discontinuity with a V-shaped depression of ∼70-160 km over a lateral distance of 600 km beneath northern South America. The shear velocity perturbations vary in the same trend showing the most pronounced reduction of ∼3-4% below the thinnest D″ layer in close proximity to an intermittently undetected discontinuity. The strong correlation between the D″ topography and velocity variations indicates the phase transition boundary has been perturbed or even disrupted by the large lateral temperature gradient of slab material which has been reheated from the core over extended periods of time.

Rolling hills on the core-mantle boundary

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, Daoyuan; Helmberger, Don V.; Jackson, Jennifer M.

2014-07-17

Recent results suggest that an iron-rich oxide may have fractionally crystallized from a primordial magma ocean and settled on the core–mantle boundary (CMB). Based on experimental results, the presence of only a few percent of Fe-rich oxide could slow seismic waves down by several percent. This heavy layer can become highly undulating as predicted from dynamic modeling but can remain as a distinct structure with uniform velocity reductions. Here, we use the large USArray seismic network to search for such structures. Strong constraints on D" are provided by the core-phase SKS where it bifurcates, containing a short segment of P-wavemore » diffractions (P d) when crossing the CMB, called SKS d. Synthetics from models with moderate velocity drops (less than 10%) involving a layer with variable thickness, perhaps a composite of sharp small structures, with strong variation in thickness can explain both the observed SKS d waveforms and large scatter in differential times between SKKS and SKS. A smooth 3D image is obtained from inverting SKS d waveforms displaying rolling-hills with elongated dome-like structures sitting on the CMB. The most prominent one has an 80-km height, ~8° length, and ~4° width, thus adding still more structural complexity to the lower mantle. We suggest that these results can be explained by a dynamically-stabilized material containing small amounts (~5%) iron-rich (Mg,Fe)O providing a self-consistent physical interpretation.« less

Lithospheric Layering beneath the Contiguous United States Constrained by S-to-P Receiver Functions

NASA Astrophysics Data System (ADS)

Liu, L.; Liu, K. H.; Kong, F.; Gao, S. S.

2017-12-01

The greatly-improved spatial coverage of broadband seismic stations as a result of the deployment of the EarthScope Transportable Array (TA) stations and the diversity of tectonic environments in the contiguous United States provide a unique opportunity to investigate the depth variation and nature of intra-lithospheric interfaces in different tectonic regimes. A total of 284,121 high-quality S-to-P receiver functions (SRFs) are obtained from 3,809 broadband seismic stations in the TA and other permanent and temporary deployments in the contiguous United States. The SRFs are computed using frequency domain deconvolution, and are stacked in consecutive circles with a radius of 2°. They are converted to depth series after move-out corrections using the IASP91 Earth model. Similar to previous SRF studies, a robust negative arrival, representing a sharp discontinuity of velocity reduction with depth, is visible in virtually all the stacked traces in the depth range of 30-110 km. Beneath the western US, the depth of this discontinuity is 69±17 km, and beneath the eastern US, it ranges from 75 to 90 km, both of which are comparable to the depth of the tomographically-determined lithosphere-asthenosphere boundary (LAB). In contrast, the depth of the discontinuity beneath the central US is 83±10 km which is significantly smaller than the 250 km LAB depth determined by seismic surface wave tomography. Based on previous seismic tomography, shear-wave splitting and mantle xenolith studies, we interpret this discontinuity as the top of a frozen-in layer of volatile-rich melt beneath the central US. The observations and the discrepancy between the SRF and seismic tomography results for the central US as well as the amplitude of the corresponding arrival on the SRFs may be explained by spatial variations of the thickness of the transitional layer between the "pure" lithosphere and the "pure" asthenosphere. Under this hypothesis, the consistency between the results from the SRFs and seismic tomography for the western and eastern US suggests a thin transitional layer. On the contrary, a thick transitional layer is inferred for the central US. For this area, while the long-period surface waves can detect the transitional layer, the gradual natural of its lower boundary makes it hard for the short wavelength SRFs to detect.

Seismic and Petrological Constraints on Deep Crustal Evolution in North America: Where and What are 7.x Layers?

NASA Astrophysics Data System (ADS)

Mahan, K. H.; Schulte-Pelkum, V.; Shen, W.; Ritzwoller, M. H.

2012-12-01

Continental crust worldwide has been found to have areas with a lowermost layer characterized by unusually high seismic P velocities of over 7 km/s, often called 7.x layers. Such layers are commonly ascribed to underplating - in some cases by underthrusting, but in most cases by magmatic processes. In North America, high-velocity lower crust underlies upper crust of Archean, Proterozoic, and younger ages. Its presence reflects the tectonic and magmatic processes associated with continental rifting, collision, subduction, and other evolutionary (e.g. thermal) trends, and its occurrence also provides clues on the nature of the underlying mantle. Detection of a lower crustal high-velocity layer stems mostly from seismic refraction and wide-angle reflection experiments, and information on its geographical extent is very spotty. Similarly sparse are age determinations and knowledge of the tectonic processes responsible for construction of these layers. Despite glimpses of 7.x layers on many profiles across the continental U.S. and Canada, there is no systematic geographical and age information on this fundamental process of crustal growth, and many of the existing observations contradict current hypotheses on underplating. We compare compositional and physical property data of lower crustal and uppermost mantle xenoliths from Montana, Wyoming, and other localities with maps of lower crustal and uppermost mantle seismic velocities obtained from joint inversions of receiver functions with surface waves, and to mapped distinct high-velocity lower crustal layers in receiver functions in areas covered by the EarthScope Transportable Array. Xenolith observations from Montana indicate that portions of metasomatized uppermost mantle exist in that area that may be difficult to distinguish from mafic lower crust based on seismic velocities alone, raising the interesting question of whether a 7.x layer may be below rather than above the seismic Moho in some cases. The persistence of high-velocity, presumably strong lower crust under the Laramide-affected Wyoming craton and the Colorado Plateau suggest that crustal strength may influence surface deformation. The Rocky Mountain Front and Rio Grande rift largely separate fast lower crust to the East from slower lower crust to the West, cutting across NE-SW trends inherited from continental assembly and suggesting that the velocity distribution may be dominated by thermal effects; however, recent volcanics do not correlate well geographically with lower crustal velocity.

Decay of Hurricanes Tracked by Dense Seismic Array

NASA Astrophysics Data System (ADS)

Lamontagne, A.; Tanimoto, T.

2014-12-01

Tropical cyclones (hurricanes and typhoons) are mostly atmospheric phenomena but they also generate significant ground motions in the solid earth when they become strong. If a dense seismological array existed along the path of a hurricane, we could learn about some processes near the hurricane eye and the change of its intensity through seismic data. We found a few cases of tropical cyclones that passed through the Transportable Array of Earthscope (TA) in the last four years. They provide some interesting time-evolving characteristics of hurricanes but in most cases seismic signals are too weak to gain any insight into the processes. The only exception we have found so far is Hurricane Isaac in 2012. Hurricane Isaac was mostly a tropical storm during its lifetime but it became a hurricane about 12 hours before the first landfall at the mouth of the Mississippi river at 0000 UTC August 29. The eye then went back over the ocean, but stayed near the coast, and made landfall again at 0800 UTC August 29. After this landfall, it went through the TA. This gave us an opportunity to study the decay of this hurricane based on seismic data. Our basic data are amplitude-distance plots for each 6-hour hurricane location. We confine our analysis to frequencies below 0.02 Hz because in higher frequency bands seismic waves were broader oceans, not necessarily near the hurricane eye. Right after the landfall, we found a sharp peak at about 75 km from the eye. This is most likely the location of the eyewall, where a strong ascending flow is known to exist. Over the next 12 hours, we see this peak deteriorate, which is undoubtedly related to the decay of the hurricane after landfall. The peak remained at the same location for these 12 hours and then in the following 18 hours started to move farther from the eye, to about 250 km. Therefore, we can monitor how the eyewall deteriorated over the 30 hours after landfall. The emphasis of this study will be on Hurricane Isaac but we will also report other cases for comparison and to clarify what we can learn about the processes near the hurricane eye by seismic data.

Dynamic triggering potential of large earthquakes recorded by the EarthScope U.S. Transportable Array using a frequency domain detection method

NASA Astrophysics Data System (ADS)

Linville, L. M.; Pankow, K. L.; Kilb, D. L.; Velasco, A. A.; Hayward, C.

2013-12-01

Because of the abundance of data from the Earthscope U.S. Transportable Array (TA), data paucity and station sampling bias in the US are no longer significant obstacles to understanding some of the physical parameters driving dynamic triggering. Initial efforts to determine locations of dynamic triggering in the US following large earthquakes (M ≥ 8.0) during TA relied on a time domain detection algorithm which used an optimized short-term average to long-term average (STA/LTA) filter and resulted in an unmanageably large number of false positive detections. Specific site sensitivities and characteristic noise when coupled with changes in detection rates often resulted in misleading output. To navigate this problem, we develop a frequency domain detection algorithm that first pre-whitens each seismogram and then computes a broadband frequency stack of the data using a three hour time window beginning at the origin time of the mainshock. This method is successful because of the broadband nature of earthquake signals compared with the more band-limited high frequency picks that clutter results from time domain picking algorithms. Preferential band filtering of the frequency stack for individual events can further increase the accuracy and drive the detection threshold to below magnitude one, but at general cost to detection levels across large scale data sets. Of the 15 mainshocks studied, 12 show evidence of discrete spatial clusters of local earthquake activity occurring within the array during the mainshock coda. Most of this activity is in the Western US with notable sequences in Northwest Wyoming, Western Texas, Southern New Mexico and Western Montana. Repeat stations (associated with 2 or more mainshocks) are generally rare, but when occur do so exclusively in California and Nevada. Notably, two of the most prolific regions of seismicity following a single mainshock occur following the 2009 magnitude 8.1 Samoa (Sep 29, 2009, 17:48:10) event, in areas with few or no known Quaternary faults and sparse historic seismicity. To gain a better understanding of the potential interaction between local events during the mainshock coda and the local stress changes induced by the passing surface waves, we juxtapose the local earthquake locations on maps of peak stress changes (e.g., radial, tangential and horizontal). Preliminary results reveal that triggering in the US is perhaps not as common as previously thought, and that dynamic triggering is most likely a more complicated interplay between physical parameters (e.g., amplitude threshold, wave orientation, tectonic environment, etc) than can be explained by a single dominant driver.

GPS data exploration for seismologists and geodesists

NASA Astrophysics Data System (ADS)

Webb, F.; Bock, Y.; Kedar, S.; Dong, D.; Jamason, P.; Chang, R.; Prawirodirdjo, L.; MacLeod, I.; Wadsworth, G.

2007-12-01

Over the past decade, GPS and seismic networks spanning the western US plate boundaries have produced vast amounts of data that need to be made accessible to both the geodesy and seismology communities. Unlike seismic data, raw geodetic data requires significant processing before geophysical interpretations can be made. This requires the generation of data-products (time series, velocities and strain maps) and dissemination strategies to bridge these differences and assure efficient use of data across traditionally separate communities. "GPS DATA PRODUCTS FOR SOLID EARTH SCIENCE" (GDPSES) is a multi-year NASA funded project, designed to produce and deliver high quality GPS time series, velocities, and strain fields, derived from multiple GPS networks along the western US plate boundary, and to make these products easily accessible to geophysicists. Our GPS product dissemination is through modern web-based IT methodology. Product browsing is facilitated through a web tool known as GPS Explorer and continuous streams of GPS time series are provided using web services to the seismic archive, where it can be accessed by seismologists using traditional seismic data viewing and manipulation tools. GPS-Explorer enables users to efficiently browse several layers of data products from raw data through time series, velocities and strain by providing the user with a web interface, which seamlessly interacts with a continuously updated database of these data products through the use of web-services. The current archive contains GDPSES data products beginning in 1995, and includes observations from GPS stations in EarthScope's Plate Boundary Observatory (PBO), as well as from real-time real-time CGPS stations. The generic, standards-based approach used in this project enables GDPSES to seamlessly expand indefinitely to include other space-time-dependent data products from additional GPS networks. The prototype GPS-Explorer provides users with a personalized working environment in which the user may zoom in and access subsets of the data via web services. It provides users with a variety of interactive web tools interconnected in a portlet environment to explore and save datasets of interest to return to at a later date. At the same time the GPS time series are also made available through the seismic data archive, where the GPS networks are treated as regular seismic networks, whose data is made available in data formats used by seismic utilities such as SEED readers and SAC. A key challenge, stemming from the fundamental differences between seismic and geodetic time series, is the representation of reprocessed of GPS data in the seismic archive. As GPS processing algorithms evolve and their accuracy increases, a periodic complete recreation of the the GPS time series archive is necessary.

Analysis of Station Quality Issues from EarthScope's Transportable Array

NASA Astrophysics Data System (ADS)

Pfeifer, C.; Barstow, N.; Busby, R.; Hafner, K.

2008-12-01

160 of the first 400 Earthscope USARRY transportable array (TA) stations have completed their first two-year deployment and are being moved to their next locations. Over the past 4 years the majority of stations have run with few interruptions in the transfer of real time data to the Array Network Facility (ANF) at the Univ of CA San Diego and near real time data to the IRIS Data Management System (DMS). The combination of telemetered data and dedicated people reviewing the waveforms and state of health data have revealed several conditions that can affect the data quality or cause loss of data. The data problems fall into three broad categories; station power, equipment malfunction, and communication failures. Station power issues have been implicated in several types of noise seen in the seismic data (as well as causing station failures and resultant data gaps). The most common type of equipment problem that has been found to degrade data quality is caused by sensor problems, and has affected all 3 types of sensors used in the TA to varying degrees. While communication problems can cause real time data loss, they do not cause a degradation of the quality of the data, and any gaps in the real time data due solely to communications problems are filled in later with the continuous data recorded to disk at each TA station. Over the past 4 years the TA team has recognized a number of noise sources and have made several design changes to minimize the effects on data quality. Design/procedural changes include: stopping water incursion into the stations, power conditioning, changing mass re-center voltage thresholds. Figures that demonstrate examples are provided. Changes have created better data quality and improved the station performance. Vigilance and deployment of service teams to reestablish communications, replace noisy sensors, and troubleshoot problems is also key to maintaining the high-quality TA network.

Seismic character of the crust and upper mantle beneath the Sierra Nevada

NASA Astrophysics Data System (ADS)

Frassetto, A.; Gilbert, H.; Zandt, G.; Owens, T. J.; Jones, C.

2008-12-01

Recent geophysical studies of the Southern Sierra Nevada suggest that the removal of a gravitationally unstable, eclogitic residue links to recent volcanism and uplift in the Eastern Sierra. The Sierra Nevada EarthScope Project (SNEP) investigates the extent of this process beneath Central and Northern Sierra Nevada. We present receiver functions, which provide estimates of crustal thickness and Vp/Vs and image the response of the crust and upper mantle to lithospheric removal. For completeness this study combines data from the 2005-2007 SNEP broadband experiment, EarthScope's BigFoot Array, regional backbone stations, and earlier PASSCAL deployments. We analyze transects of teleseismic receiver functions generated using a common-conversion-point stacking algorithm. These identify a narrow, "bright" conversion from the Moho at depths of ~25-35 km along the crest of the Eastern Sierra and adjacent Basin and Range northward to the Cascade Arc. Trade-off analysis using the primary conversion and reverberations shows a high Vp/Vs (~1.9) throughout the Eastern Sierra, which may relate to partial melt present in the lower crust. To the west the crust-mantle boundary vanishes beneath the western foothills. However, low frequency receiver functions do image the crust-mantle boundary exceeding 50 km depth along the foothills to the west and south of Yosemite National Park. Unusually deep, intraplate earthquakes (Ryan et al., this session) occur in the center of this region. The frequency dependence of the Moho conversion implies a gradational increase from crust to mantle wavespeeds over a significant depth interval. The transition from a sharp to gradational Moho probably relates to the change from a delaminated granitic crust to crust with an intact, dense, eclogitic residue. The spatial correlation and focal mechanisms of the deep earthquakes suggest that a segment of this still intact residue is currently delaminating.

Using Amplitude Ratios from Seismic Arrays for Crustal Structure, Great Earthquakes, and in Icy Environments (Invited)

NASA Astrophysics Data System (ADS)

Tsai, V. C.; Lin, F.; Duputel, Z.; Zhan, Z.

2013-12-01

Seismic amplitudes, which were previously often deemed too unreliable to use, are now more and more dependable due to advances in instrumentation, quality control measures, and improved installation procedures. With the growing availability of such reliable amplitude information, new methods can now be applied that make use of this amplitude data. Here, we discuss a number of ways we have recently applied such methods. In particular, we describe three very different situations in which we find seismic amplitude ratios to be extremely useful in constraining information that would otherwise be poorly determined. In the first application, we compute Rayleigh-wave horizontal-to-vertical (H/V) ratios for earthquakes observed across USArray, and find that imaging of upper crustal structure is improved significantly over using phase velocities alone. In addition to obtaining better constraints on shallow velocity structure, the complimentary sensitivities of H/V ratios also provide new constraints on density structure and make shallow density tomography possible. In a second application, we find that Rayleigh- and Love-wave amplitude ratios from the Mw 8.6 11 April 2012 Sumatra earthquake observed across the Global Seismographic Network provide excellent long-period constraints on the extended nature of the earthquake source. In particular, we find that the data are robustly fit by a model with two sub-events at nearly 30-km depth and with significant directivity. This multiple-point-source solution is consistent with other observations like high-frequency back projections. In a third and final application, we observe ambient-noise H/V ratios in an unusual environment on the Amery Ice Shelf, Antarctica. Unlike in most crustal settings, we find the dominant features in the H/V ratios to be unrelated to Rayleigh-wave propagation and to be instead determined by P-wave resonances in the low-velocity water layer beneath the ice. All three applications underscore the fact that seismic amplitude ratios are incredibly useful observables and can now be used routinely to help make key inferences about Earth structure and earthquake processes.

EarthScope's Transportable Array: Status of the Alaska Deployment and Guide to Resources for Lower48 Deployment

NASA Astrophysics Data System (ADS)

Busby, R. W.; Woodward, R.; Aderhold, K.; Frassetto, A.

2017-12-01

The Alaska Transportable Array deployment is completely installed, totaling 280 stations, with 194 new stations and 86 existing stations, 28 of those upgraded with new sensor emplacement. We briefly summarize the deployment of this seismic network, describe the added meteorological instruments and soil temperature gauges, and review our expectations for operation and demobilization. Curation of data from the contiguous Lower-48 States deployment of Transportable Array (>1800 stations, 2004-2015) has continued with the few gaps in real-time data replaced by locally archived files as well as minor adjustments in metadata. We highlight station digests that provide more detail on the components and settings of individual stations, documentation of standard procedures used throughout the deployment and other resources available online. In cooperation with IRIS DMC, a copy of the complete TA archive for the Lower-48 period has been transferred to a local disk to experiment with data access and software workflows that utilize most or all of the seismic timeseries, in contrast to event segments. Assembling such large datasets reliably - from field stations to a well managed data archive to a user's workspace - is complex. Sharing a curated and defined data volume with researchers is a potentially straightforward way to make data intensive analyses less difficult. We note that data collection within the Lower-48 continues with 160 stations of the N4 network operating at increased sample rates (100 sps) as part of the CEUSN, as operational support transitions from NSF to USGS.

A uniform database of teleseismic shear wave splitting measurements for the western and central United States

NASA Astrophysics Data System (ADS)

Liu, Kelly H.; Elsheikh, Ahmed; Lemnifi, Awad; Purevsuren, Uranbaigal; Ray, Melissa; Refayee, Hesham; Yang, Bin B.; Yu, Youqiang; Gao, Stephen S.

2014-05-01

We present a shear wave splitting (SWS) database for the western and central United States as part of a lasting effort to build a uniform SWS database for the entire North America. The SWS measurements were obtained by minimizing the energy on the transverse component of the PKS, SKKS, and SKS phases. Each of the individual measurements was visually checked to ensure quality. This version of the database contains 16,105 pairs of splitting parameters. The data used to generate the parameters were recorded by 1774 digital broadband seismic stations over the period of 1989-2012, and represented all the available data from both permanent and portable seismic networks archived at the Incorporated Research Institutions for Seismology Data Management Center in the area of 26.00°N to 50.00°N and 125.00°W to 90.00°W. About 10,000 pairs of the measurements were from the 1092 USArray Transportable Array stations. The results show that approximately 2/3 of the fast orientations are within 30° from the absolute plate motion (APM) direction of the North American plate, and most of the largest departures with the APM are located along the eastern boundary of the western US orogenic zone and in the central Great Basins. The splitting times observed in the western US are larger than, and those in the central US are comparable with the global average of 1.0 s. The uniform database has an unprecedented spatial coverage and can be used for various investigations of the structure and dynamics of the Earth.

Joint Inversion of Earthquake Source Parameters with local and teleseismic body waves

NASA Astrophysics Data System (ADS)

Chen, W.; Ni, S.; Wang, Z.

2011-12-01

In the classical source parameter inversion algorithm of CAP (Cut and Paste method, by Zhao and Helmberger), waveform data at near distances (typically less than 500km) are partitioned into Pnl and surface waves to account for uncertainties in the crustal models and different amplitude weight of body and surface waves. The classical CAP algorithms have proven effective for resolving source parameters (focal mechanisms, depth and moment) for earthquakes well recorded on relatively dense seismic network. However for regions covered with sparse stations, it is challenging to achieve precise source parameters . In this case, a moderate earthquake of ~M6 is usually recorded on only one or two local stations with epicentral distances less than 500 km. Fortunately, an earthquake of ~M6 can be well recorded on global seismic networks. Since the ray paths for teleseismic and local body waves sample different portions of the focal sphere, combination of teleseismic and local body wave data helps constrain source parameters better. Here we present a new CAP mothod (CAPjoint), which emploits both teleseismic body waveforms (P and SH waves) and local waveforms (Pnl, Rayleigh and Love waves) to determine source parameters. For an earthquake in Nevada that is well recorded with dense local network (USArray stations), we compare the results from CAPjoint with those from the traditional CAP method involving only of local waveforms , and explore the efficiency with bootstraping statistics to prove the results derived by CAPjoint are stable and reliable. Even with one local station included in joint inversion, accuracy of source parameters such as moment and strike can be much better improved.

Ambient Noise Correlation Amplitudes and Local Site Response

NASA Astrophysics Data System (ADS)

Bowden, D. C.; Tsai, V. C.; Lin, F. C.

2014-12-01

We investigate amplitudes from ambient noise cross correlations in a spatially dense array. Our study of wave propagation effects and ambient noise is focused on the Long Beach Array, with more than 5000 single component geophones in an area of about 100 square kilometers, providing high resolution imaging of shallow crustal features. The method allows for observations of ground properties like site response and attenuation, which can well supplement traditional velocity models and simulations for seismic hazard. Traditional ambient noise cross correlations have proven to be an effective means of measuring velocity information about surface waves, but the amplitudes of such signals in traditional processing are often distorted. We discuss a method of signal processing which preserves relative amplitudes of signals within an array, and the subsequent processing to track wave motion across the array. Previous work showed promising correlation to known local structure, but did not represent a thorough application of tomographic methods. Now we extend the methodology to more robustly consider wavefront focusing and defocusing, interference with higher modes, and discuss the differing effects of local site response, attenuation, and scattering. Application of Helmholtz tomography and determination of local site amplification has previously been demonstrated using earthquake data on the continental scale with USArray, but the exploitation of the ambient noise field is required both for the higher frequencies needed by seismic hazard studies and for the short deployment time of a Long Beach scale array. We outline both the successes and shortcomings of the methodology, and show how it can be extended for use on future arrays.

Mermaids - Mobile Earthquake Recording in Marine Areas by Independent Divers - to Mariscope.

NASA Astrophysics Data System (ADS)

Hello, Y.; Bonnieux, S.; Philippe, O.; Yegikyan, M.; Nolet, G.

2015-12-01

Mermaids are floating seismometers. The first generation used Argo floats developed for oceanographers to measure temperature and salinity. The Mermaids drift under water at about the speed of USArray and share with USArray the ability to cover a large surface. They record teleseismic P waves for events above magnitude 6.5 under noisy conditions (Indian Ocean), well below magnitude 6 under mild conditions (Mediterranean, Pacific). There are occasional recordings of PKP and PP waves. Local events can be seen down to magnitude 2. They are a perfect, low expensive and maintainable modern tool to fill the gap for monitoring the ocean. Ten mermaids have been launched May 2014 near the Galapagos to provide seismic information for deep tomography of the plume, whereas three of the Mermaids in the Mediterranean are currently being deployed/redeployed in the Ligurian Sea. These are the first launches with a purely scientific goal (as opposed to 8 earlier test deployments). Using the experience with the first fleet of prototypes, a new version is being developed. These are long-lived (five years), reach deeper (3000 m), multidisciplinary (up to eight instruments). The basic model also provides temperature and salinity data to facilitate co-financing with oceanography. In a more advanced version, it will be fully programmable by the scientist using them, and will have the ability to adapt software during missions using two-way satellite communication. If deployed in a dense array (e.g. rapid response) they obtain relative locations by sending out chirp signals between each other, surfacing from time to time for data transmission and to obtain a location and drift via GPS. They will have a "landing" capability to stay at location and monitor aftershocks while surfacing regularly for data transmission. For solo drifters, a magnetometer and a bathymetry sounder will assist in constraining the trajectory at depth.The first tests of seaworthiness of this second generation Mermaid have taken place, and a version for seismologists will be available early in 2016. Software development of the more advanced features is still under way.

Outreach to Hispanic/Latino Communities With a Spanish-Language Version of the Earthscope Website

NASA Astrophysics Data System (ADS)

López, A. M.; Stein, S.; Delaughter, J.

2005-12-01

Spanish is estimated to be the fourth language in the world based on number of speakers, the second as a vehicle of international communication and the third as an international language of politics, economics and culture. Its importance in the U.S. is illustrated by the fact that the Hispanic/Latino population is becoming the largest minority group because it has the fastest growth rate of all ethnic groups in the U.S. According to the U.S. Census Bureau, in 2004 there were ~41 million people in the U.S. (~14% of the total population) of Hispanic or Latino origin. Although the Spanish-speaking population is growing rapidly, the same cannot be said about the number of Hispanic/Latino high school and college graduates. Studies by the National Center for Education Statistics show that Hispanic/Latino students are as likely to drop out are to complete high school. Similarly, although more Hispanic/Latino students enroll in college and/or universities than a decade ago, few complete degrees. For example, in the geosciences only 3% of bachelor's degrees were granted to people identifying themselves as Hispanic or Latino. Over the last 28 years, only 263 of the 20,000 geoscience Ph.D.s awarded in the U.S. went to Hispanic Americans. Bilingual educational offerings are one technique for addressing this discrepancy. For example, scientists and research programs such as EarthScope, NASA, NOAA, and ODP frequently reach out to students and the general public using the internet. Many well-made and useful websites with scientific themes in the U.S. are available to millions of users worldwide, providing a resource that is limited or non-existent in other countries. Unfortunately, few geoscience education sites are available in languages other than English. To address this need, Earthscope is developing a Spanish version of its website describing its goals, techniques, and educational opportunities. Currently, approximately 90% of the educational content on this site (http://www.earthscope.org/education/index.php) is available in both English and Spanish. As time and resources permit, more of the site will be translated. This effort is already having an effect; in a recent Google search using the term "Ferias Científicas" (Science Fairs), EarthScope's site ranked second. Such Spanish material will hopefully have several applications relevant to Earthscope goals. They should encourage Spanish-speaking students to explore the geosciences, and help Hispanic populations become more knowledgeable about the Earth by providing information about the geologic processes and hazards in their area in a language they truly understand. In addition, such web sites can provide useful resources to people in Latin American countries, many of which have geologic processes that are an important aspect of their lives.

Promoting seismology education through collaboration between university research scientists and school teachers

NASA Astrophysics Data System (ADS)

Brunt, M. R.; Ellins, K. K.; Boyd, D.; Mote, A. S.; Pulliam, J.; Frohlich, C. A.

2012-12-01

Participation in the NSF-sponsored Texas Earth and Space Science (TXESS) Revolution teacher professional development project paved the way for several teachers to receive educational seismometers and join the IRIS Seismograph in Schools program. This, in turn, has led to secondary school teachers working with university seismologists on research projects. Examples are the NSF-EarthScope SIEDCAR (Seismic Investigation of Edge Driven Convection Associated with the Rio Grande Rift) project; field studies to compile felt-reports for Texas earthquakes, some which may have been induced by human activities; and a seismic study of the Texas Gulf Coast to investigate ocean-continent transition processes along a passive margin. Such collaborations are mutually beneficial in nature. They help scientists to accomplish their research objectives, involve teachers and their students in the authentic, inquiry-based science, promote public awareness of such projects, and open the doors to advancement opportunities for those teachers involved. In some cases, bringing together research scientists and teachers results in collaborations that produce publishable research. In order to effectively integrate seismology research into 7-12 grade education, one of us (Brunt) established the Eagle Pass Junior High Seismology Team in connection with IRIS Seismograph in Schools, station EPTX (AS-1 seismograph), to teach students about earthquakes using authentic real-time data. The concept has sparked interest among other secondary teachers, leading to the creation of two similarly organized seismology teams: WPTX (Boyd, Williams Preparatory School, Dallas) and THTX (Mote, Ann Richards School for Young Women Leaders, Austin). Although the educational seismometers are basic instruments, they are effective educational tools. Seismographs in schools offer students opportunities to learn how earthquakes are recorded and how modern seismometers work, to collect and interpret seismic data, and to experiment with ground shaking. Recognizing this value, researchers in Texas have proposed to create, maintain and promote a Texas Educational Seismic Network (TESN) as a legacy of the NSF-funded EarthScope program. If funding is obtained, 15 educational seismometers will be added to the existing network of 12 to include more university and two-year college (2YC) faculty, and secondary teachers as operators. University operators would partner with and support nearby secondary and 2YC operators.

Lower-mantle plume beneath the Yellowstone hotspot revealed by core waves

NASA Astrophysics Data System (ADS)

Nelson, Peter L.; Grand, Stephen P.

2018-04-01

The Yellowstone hotspot, located in North America, is an intraplate source of magmatism the cause of which is hotly debated. Some argue that a deep mantle plume sourced at the base of the mantle supplies the heat beneath Yellowstone, whereas others claim shallower subduction or lithospheric-related processes can explain the anomalous magmatism. Here we present a shear wave tomography model for the deep mantle beneath the western United States that was made using the travel times of core waves recorded by the dense USArray seismic network. The model reveals a single narrow, cylindrically shaped slow anomaly, approximately 350 km in diameter that we interpret as a whole-mantle plume. The anomaly is tilted to the northeast and extends from the core-mantle boundary to the surficial position of the Yellowstone hotspot. The structure gradually decreases in strength from the deepest mantle towards the surface and if it is purely a thermal anomaly this implies an initial excess temperature of 650 to 850 °C. Our results strongly support a deep origin for the Yellowstone hotspot, and also provide evidence for the existence of thin thermal mantle plumes that are currently beyond the resolution of global tomography models.

Revised Earthquake Catalog and Relocated Hypocenters Near Fluid Injection Wells and the Waste Isolation Pilot Plant (WIPP) in Southeastern New Mexico

NASA Astrophysics Data System (ADS)

Edel, S.; Bilek, S. L.; Garcia, K.

2014-12-01

Induced seismicity is a class of crustal earthquakes resulting from human activities such as surface and underground mining, impoundment of reservoirs, withdrawal of fluids and gas from the subsurface, and injection of fluids into underground cavities. Within the Permian basin in southeastern New Mexico lies an active area of oil and gas production, as well as the Waste Isolation Pilot Plant (WIPP), a geologic nuclear waste repository located just east of Carlsbad, NM. Small magnitude earthquakes have been recognized in the area for many years, recorded by a network of short period vertical component seismometers operated by New Mexico Tech. However, for robust comparisons between the seismicity patterns and the injection well locations and rates, improved locations and a more complete catalog over time are necessary. We present results of earthquake relocations for this area by using data from the 3-component broadband EarthScope Flexible Array SIEDCAR experiment that operated in the area between 2008-2011. Relocated event locations tighten into a small cluster of ~38 km2, approximately 10 km from the nearest injection wells. The majority of events occurred at 10-12 km depth, given depth residuals of 1.7-3.6 km. We also present a newly developed more complete catalog of events from this area by using a waveform cross-correlation algorithm and the relocated events as templates. This allows us to detect smaller magnitude events that were previously undetected with the short period network data. The updated earthquake catalog is compared with geologic maps and cross sections to identify possible fault locations. The catalog is also compared with available well data on fluid injection and production. Our preliminary results suggest no obvious connection between seismic moment release, fluid injection, or production given the available monthly industry data. We do see evidence in the geologic and well data of previously unidentified faults in the area.

SPREE: A Successful Seismic Array by a Failed Rift System; Analysis of Seismic Noise in the Seismically Quiet Mid-continent

NASA Astrophysics Data System (ADS)

Wolin, E.; van der Lee, S.; Bollmann, T. A.; Revenaugh, J.; Aleqabi, G. I.; Darbyshire, F. A.; Frederiksen, A. W.; Wiens, D.; Shore, P.

2014-12-01

The Superior Province Rifting Earthscope Experiment (SPREE) completed its field recording phase last fall with over 96% data return. While 60% of the stations returned data 100% of the time, only 9 performed below 90% and one station had questionable timing. One station was vandalized, another stolen. One station continued recording after its solar panels were pierced by a bullet, while another two stations survived a wildfire and a blow-down, respectively. The blow-down was an extreme wind event that felled hundreds of thousands of trees around the station. SPREE stations recorded many hundreds of earthquakes. Two regional earthquakes and over 400 teleseismic earthquakes had magnitudes over 5.5 and three, smaller local earthquakes had magnitudes over 2.5. We have calculated power spectral estimates between 0.1-1000 s period for the ~2.5-year lifespan of all 82 SPREE stations. Vertical channels performed quite well across the entire frequency range, falling well below the high noise model of Peterson (1993) and usually within 10-15 dB of nearby Transportable Array stations. SPREE stations' horizontal components suffer from long-period (> 30 s) noise. This noise is quietest at night and becomes up to 30 dB noisier during the day in the summer months. We explore possible causes of this variation, including thermal and atmospheric pressure effects. One possibility is that stations are insulated by snow during the winter, reducing temperature variations within the vault. Spring snowmelt creates instability at many of the SPREE stations, evidenced by frequent recenterings and enhanced long-period noise. For all channels, power in the microseismic band (4-16 s) is strongest in the winter, corresponding to storm season in the Northern Hemisphere, and approximately 20 dB weaker during the summer. The power spectrum and temporal variation of microseismic energy is consistent across the entire SPREE array.

Determination of Rayleigh wave ellipticity using single-station and array-based processing of ambient seismic noise

NASA Astrophysics Data System (ADS)

Workman, Eli Joseph

We present a single-station method for the determination of Rayleigh wave ellipticity, or Rayleigh wave horizontal to vertical amplitude ratio (H/V) using Frequency Dependent Polarization Analysis (FDPA). This procedure uses singular value decomposition of 3-by-3 spectral covariance matrices over 1-hr time windows to determine properties of the ambient seismic noise field such as particle motion and dominant wave-type. In FPDA, if the noise is mostly dominated by a primary singular value and the phase difference is roughly 90° between the major horizontal axis and the vertical axis of the corresponding singular vector, we infer that Rayleigh waves are dominant and measure an H/V ratio for that hour and frequency bin. We perform this analysis for all available data from the Earthscope Transportable Array between 2004 and 2014. We compare the observed Rayleigh wave H/V ratios with those previously measured by multicomponent, multistation noise cross-correlation (NCC), as well as classical noise spectrum H/V ratio analysis (NSHV). At 8 sec the results from all three methods agree, suggesting that the ambient seismic noise field is Rayleigh wave dominated. Between 10 and 30 sec, while the general pattern agrees well, the results from FDPA and NSHV are persistently slightly higher ( 2%) and significantly higher (>20%), respectively, than results from the array-based NCC. This is likely caused by contamination from other wave types (i.e., Love waves, body waves, and tilt noise) in the single station methods, but it could also reflect a small, persistent error in NCC. Additionally, we find that the single station method has difficulty retrieving robust Rayleigh wave H/V ratios within major sedimentary basins, such as the Williston Basin and Mississippi Embayment, where the noise field is likely dominated by reverberating Love waves.

Preliminary Results of Crustal Structure beneath the Wabash Valley Seismic Zone Using Teleseismic Receiver Functions and Ambient Noise Tomography

NASA Astrophysics Data System (ADS)

Zhu, L.; Aziz Zanjani, A.; Hu, S.; Liu, Y.; Herrmann, R. B.; Conder, J. A.

2015-12-01

As part of a on-going EarthScope FlexArray project, we deployed 45 broadband seismographs in a 300-km-long linear profile across the Wabash Valley Seismic Zone (WVSZ). Here we present preliminary results of crustal structure beneath WVSZ based on teleseismic receiver functions and ambient noise tomography. We combined waveform data of the temporary stations in 2014 with those of permanent seismic stations and the transportable array stations in our study area since 2011. We found 656 teleseismic events with clear P-wave signals and obtained 2657 good-quality receiver functions of 84 stations using a time-domain iterative deconvolution method. We estimated crustal thickness and Vp/Vs ratio beneath each station using the H-κ stacking method. A high-resolution crustal structural image along the linear profile was obtained using the Common-Conversion-Point (CCP) stacking method. We also measured Rayleigh-wave phase and group velocities from 5 to 50 s by cross-correlating ambient noises between stations and did joint-inversion of receiver functions and surface wave dispersions for S-velocity structures beneath selected stations. The results show that the average crustal thickness in the region is 47 km with a gentle increase of crustal thickness from southeast to northwest. A mid-crustal interface is identified in the CCP image that also deepens from 15 km in the southeastern end to >20 km in the northwest. The CCP image shows that the low-velocity sedimentary layer along the profile is broad and is thickest (~10 km) near the center of the Wabash Valley. Beneath the center of the Valley there is a 40-km-wide positive velocity discontinuity at a depth of 40 km in the lower crust that might be the top of a rift pillow in this failed continental rift. Further results using 3D joint inversion and CCP migration will be presented at the meeting.

Increasing Geoscience Literacy and Public Support for the Earthscope National Science Initiative Through Informal Education

NASA Astrophysics Data System (ADS)

Aubele, J. C.

2005-12-01

Geology and geophysics are frequently perceived by the student, teacher, or adult non-geologist as "difficult to understand"; however, most non-geologists of all ages appreciate geological landforms such as mountains, volcanoes and canyons, and are interested in phenomena such as earthquakes and natural resources. Most people are also interested in local connections and newsworthy programs and projects. Therefore, the EarthScope Project is a perfect opportunity to excite and educate the public about solid-Earth geoscience research and to increase the non-geologist's understanding of Earth's dynamic processes. As the EarthScope Project sweeps across the country, the general public must be made aware of the magnitude, scope, excitement, and achievements of this national initiative. However, EarthScope science is difficult for the non-scientist to understand. The project is large-scale and long-term, and its data sets consist of maps, structural graphics, 3D and 4D visualizations, and the integration of many different geophysical instruments, all elements that are difficult for the non-scientist to understand. Targeted programs for students, teachers, and visitors to the National Parks will disseminate EarthScope information; in addition, museums and other informal science education centers can also play an important role in translating scientific research for the general public. Research on learning in museums has shown that museums educate an audience that is self-selected and self-directed (non-captive), includes family/groups, multigenerational, and repeat visitors, and requires presentation of information for a variety of learning styles. Informal science centers have the following advantages in geoscience-related education: (1) graphics/display expertise; (2) flexibility in approach and programming; (3) ability to quickly produce exhibits, educational programming, and curricula themed to specific topics of interest; (4) inclusion of K-12 teachers in the development of educational programs and materials for students, pre-service and in-service teachers, (5) family learning opportunities; (6) community-wide audience ranging from pre-K through Senior Citizen; (7) accessible, visitor-friendly and non-threatening resource site for science information for the community. Museums and other science centers provide concise, factual, reliable and entertaining presentations of the relevant information. It is not enough to simply report on the scientific research, museums educate through object-based and inquiry-based learning and experiential programming.

Out-of-plane reflections - are they evidence for deep subducted lithosphere?

NASA Astrophysics Data System (ADS)

Schumacher, Lina; Thomas, Christine

2015-04-01

Subduction zones form dominant tectonic features on the Earth and have complex three-dimensional structures. Tomographic inversions for P- and S-wave seismic velocities in the Earth's mantle give impressive images of slabs descending into the deep Earth. However, direct observations of deep slabs are scarce but necessary to make statements concerning physical parameters, structural differences within the slab and its behavior with depth. The main objective of this study is to investigate the geometry, physical parameters and structural differences of subducted lithosphere by investigating seismic P-wave arrivals that reflect off the base of the slab using seismic array techniques. The great circle paths of the source-receiver combinations used do not intersect the slab and serve as reference. We focus on the North pacific region by using earthquakes from Japan, the Philippines and the Hindukush recorded at North American networks (e.g. USArray, Alaska and Canada). The data cover a period from 2000-2012 with a minimum magnitude of 5.6 Mw and depths below 100 km. We are looking for reflections from the slab region that would arrive at the stations with deviating backazimuths. Information on slowness, backazimuth and travel time of the observed out-of-plane arrivals is used to backtrace the wave to its scattering location and to map seismic heterogeneities associated with subduction zones. The reflection points give an idea for the 3D structures within the mantle. Assuming only single scattering in the backtracing algorithm, most out-of-plane signals have to travel as P*P and only a few as S*P phases, due to their timing. Taking into account the radiation pattern of each event in direction of the great circle path and towards the calculated reflection point, it is possible to compare the polarities of the out-of-plane signals with P and/or PP. Furthermore, we analyze the out-of-plane waveforms in the beam trace of the observed slowness and backazimuth by cross-correlating them with great circle path phases and applying a systematic frequency analysis. Since the backtracing results are used for the further analysis of the signals, it is important to know how robust the backtracing routine is. We therefore analyze synthetic seismograms for 3D models with and without slab like heterogeneities. The result helps us to understand the depth dependent thermal behavior of sinking lithosphere, its internal structure and the extent to which it is seismically visible.

Academia vs Industry: vanishing boundaries between global earthquake seismology and exploration seismics.

NASA Astrophysics Data System (ADS)

van der Hilst, R. D.

2011-12-01

Global seismology and exploration seismics have long lived in parallel universes, with little cross-fertilization of methodologies and with interaction between the associated communities often limited to company recruitment of students. Fortunately, this traditional separation of technology and people has begun to disappear. This is driven not only by continuing demands for human and financial resources (for companies and academia, respectively) but increasingly also by overlapping intellectual interest. First, 'waves are waves' (that is, the fundamental physics - and math to describe/handle it - is scale invariant) and many artificial boundaries are being removed by use of better wave theory, faster computers, and new data acquisition paradigms. For example, the development of dense sensor arrays (in USA, Europe, Asia - mostly China and Japan) is increasing the attraction (and need) of industry-style interrogation of massive data sets. Examples include large scale seismic exploration of Earth's deep interior with inverse scattering of teleseismic wavefields (e.g., Van der Hilst et al., Science, 2007). On the other hand, reservoir exploration and production benefits from expertise in earthquake seismology, both for better characterization of reservoirs and their overburden and for (induced) micro-earthquake analysis. Passive source methods (including but not restricted to ambient noise tomography) are providing new, economic opportunities for velocity analysis and monitoring, and studies of (micro)seismicity (e.g., source location, parameters, and moment tensor) allow in situ stress determination, tomographic velocity analysis with natural sources in the reservoir, and 4D monitoring (e.g., for hydrocarbon production, carbon sequestration, enhanced geothermal systems, and unconventional gas production). Second, the gap between the frequency ranges traditionally considered by both communities is being bridged by better theory, new sensor technology, and through extraction of new types of data, for instance through seismic interferometry (including ambient noise correlations). Third, there is growing interest in the same type of problem, from reservoir to continental scale. For instance, USArray enables systematic imaging (at basin scale and beyond) of continental crust, which is of interest for frontier exploration of natural resources companies, whereas the latter have many resources, including unique data sets and expertise, that can be used by the academic communities to improve multi-scale characterization and interpretation. The main challenge for successful interaction is the recognition of problems of common interest, the management of expectations (for instance concerning the types of problems students can work on and time scales of delivery), and the establishment of the right model for interaction. My presentation will be informed by my experience with energy companies as Director of MIT's Earth Resources Laboratory.

PBO Nucleus Project Summary: The Successful Integration of 209 Existing GPS Sions in the Plate Boundary Observatory

NASA Astrophysics Data System (ADS)

Blume, F.; Miller, M.; Boyce, E.; Borsa, A.; Eriksson, S.

2008-12-01

Tectonic and earthquake research in the US has experienced a quiet revolution over the last decade precipitated by the recognition that slow-motion faulting events can both trigger and be triggered by regular earthquakes. Transient motion has now been found in essentially all tectonic environments, and the detection and analysis of such events is the first-order science target of the EarthScope Project. Because of this and a host of other fundamental tectonics questions that can be answered only with long-duration geodetic time series, the 1100-station EarthScope Plate Boundary Observatory (PBO) network was designed to leverage 445 existing continuous GPS stations whose measurements extend back over a decade. The irreplaceable recording history of these stations will accelerate EarthScope scientific return by providing the highest possible resolution. This resolution will be used to detect and understand transients, to determine the three-dimensional velocity field (particularly vertical motion), and to improve measurement precision by understanding the complex noise sources inherent in GPS. The PBO Nucleus project supports the operation, maintenance and hardware upgrades of a subset of the six western U.S. geodetic networks until they are subsumed by PBO. Uninterrupted data flow from these stations will effectively double the time-series length of PBO over the expected life of EarthScope, and has created, for the first time, a single GPS-based geodetic network in the US. The other existing sites remain in operation under support from non-NSF sources (e.g. the USGS), and EarthScope continues to benefit from their continued operation On the grounds of relevance to EarthScope science goals, geographic distribution and data quality, 209 of the 432 existing stations were selected as the nucleus upon which to build PBO. Conversion of these stations to a PBO-compatible mode of operation was begun under previous funding, and as a result data now flow directly to PBO archives and processing centers while maintenance, operations, and meta-data requirements are continue to be upgraded to PBO standards. At the end of this project all 209 stations have been fully incorporated into PBO, meeting all standards for new PBO construction including data communications and land use permits. Funds for operation of these stations have been included in approved budgets for PBO's Operations and Maintenance phase. The data from these stations serve a much larger audience than just the few people who work to keep them operating. This project is now collecting the data that will be used by the next generation of solid-earth researchers for at least two decades. Educational modules are being developed by a team of researchers, educators, and curriculum development professionals, and are being disseminated through regional and national workshops. An interactive website provides the newest developments in tectonics research to K-16 classrooms. class="ab'>

Multi-mode phase speed measurements with array-based analysis: Application to the North American continent

NASA Astrophysics Data System (ADS)

Matsuzawa, H.; Yoshizawa, K.

2017-12-01

Recent high-density broad-band seismic networks allow us to construct improved 3-D upper mantle models with unprecedented horizontal resolution using surface waves. Such dispersion measurements have been primarily based on the analysis of fundamental mode. Higher-mode information can be of help in enhancing vertical resolution of 3-D models, but their dispersion analysis is intrinsically difficult, since wave-packets of several modes are overlapped each other in an observed seismogram. In this study, we measure phase dispersion of multi-mode surface waves with an array-based analysis. Our method is modeled on a one-dimensional frequency-wavenumber method originally developed by Nolet (1975, GRL), which can be applied to a set of broadband seismic records observed in a linear array along a great circle path. Through this analysis, we can obtain a spectrogram in c-T (phase speed - period) domain, which is characterized by mode-branch dispersion curves and relative spectral powers for each mode. Synthetic experiments indicate that we can separate the modal contribution using a long linear array with typical array length of about 2000 to 4000 km. The method is applied to a large data set from USArray using nearly 400 seismic events in 2007 - 2014 with Mw 6.5 or greater. Our phase-speed maps for the fundamental-mode Love and Rayleigh waves and the first higher-mode Rayleigh waves match well with the earlier models. The phase speed maps reflect typical large-scale features of regional seismic structure in North America, but smaller-scale variations are less constrained in our model, since our measured phase speeds represent path-average features over a long path (about a few thousands kilometers). Our multi-mode dispersion measurements can also be used for the extraction of mode-branch waveforms for the first a few modes. This can be done by applying a narrow filter around the dispersion curves of a target mode in c-T spectrogram. The mode-branch waveforms can then be reconstructed based on a linear Radon transform (e.g., Luo et al., 2015, GJI). Synthetic experiments suggest that we can successfully retrieve the mode-branch waveforms for several mode branches, which can be used in the secondary analysis for constraining local-scale heterogeneity with enhanced depth resolution.

Development of the AuScope Australian Earth Observing System

NASA Astrophysics Data System (ADS)

Rawling, T.

2017-12-01

Advances in monitoring technology and significant investment in new national research initiatives, will provide significant new opportunities for delivery of novel geoscience data streams from across the Australian continent over the next decade. The AuScope Australian Earth Observing System (AEOS) is linking field and laboratory infrastructure across Australia to form a national sensor array focusing on the Solid Earth. As such AuScope is working with these programs to deploy observational infrastructure, including MT, passive seismic, and GNSS networks across the entire Australian Continent. Where possible the observational grid will be co-located with strategic basement drilling in areas of shallow cover and tied with national reflection seismic and sampling transects. This integrated suite of distributed earth observation and imaging sensors will provide unprecedented imaging fidelity of our crust, across all length and time scales, to fundamental and applied researchers in the earth, environmental and geospatial sciences. The AEOS will the Earth Science community's Square Kilometer Array (SKA) - a distributed telescope that looks INTO the earth rather than away from it - a 10 million SKA. The AEOS is strongly aligned with other community strategic initiatives including the UNCOVER research program as well as other National Collaborative Research Infrastructure programs such as the Terrestrial Environmental Research Network (TERN) and the Integrated Marine Observing System (IMOS) providing an interdisciplinary collaboration platform across the earth and environmental sciences. There is also very close alignment between AuScope and similar international programs such as EPOS, the USArray and EarthCube - potential collaborative linkages we are currently in the process of pursuing more fomally. The AuScope AEOS Infrastructure System is ultimately designed to enable the progressive construction, refinement and ongoing enrichment of a live, "FAIR" four-dimensional Earth Model for the Australian Continent and its immediate environs.

Nucleation and kinematic rupture of the 2017 Mw 8.2 Chiapas Mexico earthquake

NASA Astrophysics Data System (ADS)

Meng, L.; Huang, H.; Xie, Y.; Feng, T.; Dominguez, L. A.; Han, J.; Davis, P. M.

2017-12-01

Integrated geophysical observations from the 2017 Mw 8.2 Oaxaca, Mexico earthquake allow the exploration of one of the largest recorded normal faulting events inside a subducting slab. In this study, we collect seismic data from regional and teleseismic stations, and regional tsunami recordings to better understand the preparation and rupture processes. The mainshock occurred on the steeply dipping plane of a mega-normal fault, confirmed by time reversal analysis of tsunami waves. We utilize a template matching approach to detect possible missing earthquakes within a 2-month period before the Oaxaca mainshock. The seismicity rate (M > 3.7) shows an abrupt increase in the last day within 30 km around the mainshock hypocenter. The largest one is a M 4.6 event with similar normal faulting as the mainshock located at about 18 km updip from the hypocenter. The waveforms of the subsequent foreshocks are not similar, supporting the diversity of their locations or focal mechanisms. The nucleation process can be explained by a cascading process which eventually triggers the mainshock. Back-projection using the USArray network in Alaska reveals that the mainshock rupture propagated northwestward unilaterally at a speed of 3.1 km/s, for about 200 km and terminated near the Tehuantepec Fracture Zone. We also document the tectonic fabric of bending related faulting of the incoming Cocos plate. The mainshock is likely a reactivation of subducted outer rise faults, supported by the similarity of the strike angle between the mainshock and the outer rise faults. The surprisingly large magnitude is consistent with the exceedingly large dimensions of outer rise faulting in this particular segment of the central Mexican trench.

Global Seismic Imaging Based on Adjoint Tomography

NASA Astrophysics Data System (ADS)

Bozdag, E.; Lefebvre, M.; Lei, W.; Peter, D. B.; Smith, J. A.; Zhu, H.; Komatitsch, D.; Tromp, J.

2013-12-01

Our aim is to perform adjoint tomography at the scale of globe to image the entire planet. We have started elastic inversions with a global data set of 253 CMT earthquakes with moment magnitudes in the range 5.8 ≤ Mw ≤ 7 and used GSN stations as well as some local networks such as USArray, European stations, etc. Using an iterative pre-conditioned conjugate gradient scheme, we initially set the aim to obtain a global crustal and mantle model with confined transverse isotropy in the upper mantle. Global adjoint tomography has so far remained a challenge mainly due to computational limitations. Recent improvements in our 3D solvers (e.g., a GPU version) and access to high-performance computational centers (e.g., ORNL's Cray XK7 "Titan" system) now enable us to perform iterations with higher-resolution (T > 9 s) and longer-duration (200 min) simulations to accommodate high-frequency body waves and major-arc surface waves, respectively, which help improve data coverage. The remaining challenge is the heavy I/O traffic caused by the numerous files generated during the forward/adjoint simulations and the pre- and post-processing stages of our workflow. We improve the global adjoint tomography workflow by adopting the ADIOS file format for our seismic data as well as models, kernels, etc., to improve efficiency on high-performance clusters. Our ultimate aim is to use data from all available networks and earthquakes within the magnitude range of our interest (5.5 ≤ Mw ≤ 7) which requires a solid framework to manage big data in our global adjoint tomography workflow. We discuss the current status and future of global adjoint tomography based on our initial results as well as practical issues such as handling big data in inversions and on high-performance computing systems.

Using EarthScope Data to Engage Teachers in Research

NASA Astrophysics Data System (ADS)

Richardson, E.; McGuire, J. J.; Rubio, E.; Newton, M. H.; Hardwig, M. D.; Kraft, R. L.

2012-12-01

An overarching goal of the Master of Education in Earth Sciences program at Penn State University is to expose excellent and enthusiastic teachers to primary scientific research in Earth and space science so they can master educational objectives and translate their own discoveries directly back to their classrooms. Since 2010, teachers in the program have collaborated with research scientists at Penn State and the Woods Hole Oceanographic Institution in research efforts focused on EarthScope data. We have investigated the connection between seismic strain transients and earthquake swarms in the western United States using a combination of Plate Boundary Observatory Global Positioning System data and earthquake catalog data. The Next Generation Science Standards emphasize a learning process that is much more closely aligned with the way scientists actually conduct research, but secondary teachers are often not given the opportunity for the professional development necessary to implement this style of teaching. We observe that one of the best ways to achieve this goal is for teachers to do research. The teachers who participated in this project have asserted that their experience not only enhanced their content knowledge but also gave them a true appreciation about "the way science really works." Previous studies confirm our anecdotal observation that teacher participation in fundamental research translates to student success, although few longitudinal studies exist. We are in the process of creating an Open Educational Resources database that features downloadable lesson plans sorted by subject, grade level, and learning standard based on the EarthScope-data-driven current research our project has produced. It is a testament to the skills and depth of content mastery of these teachers that they have engaged in cutting edge research and have also distilled it, and repurposed it so that it can be taught to and shared with their own middle and high school students. The next challenge for research scientists is to scale up efforts such as ours so that more than a mere handful of secondary teachers can participate in real science.

Noise Characteristics of EarthScope Transportable Array Posthole Sensor Emplacements in Alaska and Canada

NASA Astrophysics Data System (ADS)

Aderhold, K.; Frassetto, A.; Busby, R. W.; Enders, M.; Bierma, R. M.; Miner, J.; Woodward, R.

2016-12-01

From 2011 to 2015, IRIS has built or upgraded 67 broadband seismic stations in Alaska and western Canada as part of the EarthScope Transportable Array (TA) program. An additional 72 stations will be completed by the fall of 2016. Nearly all use new posthole seismometers, emplaced at 3 m depth in cased holes within fractured bedrock outcrops, permafrost, or soil. Based on initial tests in Alaska, New Mexico, and California, this emplacement technique was chosen to streamline logistics in challenging, remote conditions as well as optimize station performance. A versatile drill capable of operating with a hammer bit or auger was developed specifically for the TA and is light enough to be transported by helicopter in a single load. The drilling system is ideal for TA deployment logistics in Alaska, but could be adapted to many regional or permanent network operations because it is easily transported on a flatbed truck and manuevered into tight working locations. The TA will complete another 73 installations in 2017 and operate the full network of 268 real-time stations through at least 2019. The removal of some TA stations is planned for 2020, but upgrades to existing stations are permanent contributions to these networks. The TA stations are a proof of concept for a new approach to emplacement of seismometers across a large network and will enable high-quality scientific research as well as advances in hazard monitoring. To evaluate the new and upgraded stations, we use probability density functions of hourly power spectral density computed by the IRIS DMC MUSTANG metric service for the continuous data recorded through 2016. Our results show that the noise performance of TA postholes in Alaska and Canada show significant improvement over the tank vaults of the lower-48 TA. With an ideal posthole drilled into bedrock or permafrost, noise levels can approach the quality of GSN stations particularly on the horizontal channels at long periods [>70 seconds]. Stations also display a strong but expected regional and seasonal variation. We provide notable examples of station performance, focusing on regional trends as well as the performance of stations upgraded from surface vault to posthole configuration.

Teachers Engaged in Authentic EarthScope Research: Challenges and Successes (Invited)

NASA Astrophysics Data System (ADS)

Richardson, E.

2013-12-01

Since 2010, eight teachers from five different states who are enrolled in the Master of Education in Earth Sciences program at Penn State University have collaborated with research scientists at Penn State and the Woods Hole Oceanographic Institution in an NSF-funded research effort focused on EarthScope data. We have investigated the connection between seismic strain transients and earthquake swarms in the western United States using a combination of Plate Boundary Observatory global positioning system data and earthquake catalog data. The participating teachers have not only taken an active role in the research but have designed classroom-ready lessons and activities they have taught to their own students. Here I discuss the challenges and successes of this project, emphasizing those I believe to be applicable to any scientist hoping to develop a similar project. Foremost, university scientists are largely unfamiliar with mentoring teachers (or any adult learners who are not planning to become researchers) in the process of doing science. Therefore, project design requires careful planning, as the background knowledge and quantitative skills of the participating teachers can vary considerably. It is important to strike a balance between manageable scope and likelihood of achieving worthwhile scientific results. Furthermore, PSU's M.Ed. in Earth Sciences program is fully online--the teacher participants are all at a distance. We prevailed over this challenge largely because the project involved analysis of digital data, making it naturally suited for asynchronous electronic collaboration and communication. The other important basis of success of this project involved distribution of labor. We analyzed data from different geographic regions and over different time periods, so each teacher participant had ownership of and gained expertise about a specific portion of the project, and the parts naturally summed to the whole. The teachers who participated in this research have asserted that their experience not only enhanced their content knowledge but also gave them a true appreciation about 'the way science really works,' and they have enthusiastically transmitted this knowledge to their own students.

Transfer of New Earth Science Understandings to Classroom Teaching: Lessons Learned From Teachers on the Leading Edge

NASA Astrophysics Data System (ADS)

Butler, R.; Ault, C.; Bishop, E.; Southworth-Neumeyer, T.; Magura, B.; Hedeen, C.; Groom, R.; Shay, K.; Wagner, R.

2006-05-01

Teachers on the Leading Edge (TOTLE) provided a field-based teacher professional development program that explored the active continental margin geology of the Pacific Northwest during a two-week field workshop that traversed Oregon from the Pacific Coast to the Snake River. The seventeen teachers on this journey of geological discovery experienced regional examples of subduction-margin geology and examined the critical role of geophysics in connecting geologic features with plate tectonic processes. Two examples of successful transfer of science content learning to classroom teaching are: (1) Great Earthquakes and Tsunamis. This topic was addressed through instruction on earthquake seismology; field observations of tsunami geology; examination of tsunami preparedness of a coastal community; and interactive learning activities for children at an Oregon Museum of Science and Industry (OMSI) Science Camp. Teachers at Sunnyside Environmental School in Portland developed a story line for middle school students called "The Tsunami Hotline" in which inquiries from citizens serve as launch points for studies of tsunamis, earthquakes, and active continental margin geology. OMSI Science Camps is currently developing a new summer science camp program entitled "Tsunami Field Study" for students ages 12-14, based largely on TOTLE's Great Earthquakes and Tsunamis Day. (2) The Grand Cross Section. Connecting regional geologic features with plate tectonic processes was addressed many times during the field workshop. This culminated with teachers drawing cross sections from the Juan de Fuca Ridge across the active continental margin to the accreted terranes of northeast Oregon. Several TOTLE teachers have successfully transferred this activity to their classrooms by having student teams relate earthquakes and volcanoes to plate tectonics through artistic renderings of The Grand Cross Section. Analysis of program learning transfer to classroom teaching (or lack thereof) clearly indicates the importance of pedagogical content knowledge and having teachers share their wisdom in crafting new earth science content knowledge into learning activities. These lessons and adjustments to TOTLE program goals and strategies may be valuable to other Geoscience educators seeking to prepare K-12 teachers to convey the discoveries of EarthScope's USArray and Plate Boundary Observatory experiments to their students.

Magmatism and underplating, a broadband seismic perspective on the Proterozoic tectonics of the Great Falls and Snowbird Tectonic Zones

NASA Astrophysics Data System (ADS)

Chen, Y.; Gu, Y. J.; Dokht, R.; Wang, R.

2017-12-01

The crustal and lithospheric structures beneath the Western Canada Sedimentary Basin (WCSB) and northern Montana contain vital records of the Precambrian tectonic development of Laurentia. In this study, we analyze the broadband seismic data recorded by the USArray and the most complete set of regional seismic networks to date near the WCSB. We adopt an integrated approach to investigate crustal structure and history, based primarily on P-to-S receiver functions but incorporate results from noise correlation functions, finite-frequency tomography and potential field measurements. In comparison with existing regional and global models, our stacked receiver functions show considerable improvements in the resolution of both Moho depth and Vp/Vs ratio. We identify major variations in Moho depth from the WCSB to the adjacent Cordillera. The Moho deepens steeply from 40 km in the Alberta basin to 50 km beneath the foothills, following Airy isostasy, but thermal buoyancy may be responsible for a flat, shallow ( 35 km) Moho to the west of the Rocky Mountain Trench. The Moho depth also increases sharply near the Snowbird Tectonic Zone (STZ), which is consistent with earlier findings from active-source data. Multiple lower crustal phases, a high velocity shallow mantle and elevated Vp/Vs ratios along the westernmost STZ jointly suggest major Proterozoic subduction and magmatism along this collisional boundary. In northern Montana, the Moho deepens along the Great Falls Tectonic Zone (GFTZ), a proposed Proterozoic suture between the Medicine Hat Block and Wyoming craton. This transition occurs near the Little Belt Mountain, which is located south of the Great Falls Shear Zone, an extensive northeast striking fault system characterized by strong potential field gradients. Similar to the STZ, our receiver functions offer new evidence for Proterozoic underplating in the vicinity of the GFTZ. In view of similar rock ages near the collisional boundaries in all parts of northern Montana and the WCSB basement, we conjecture that the Rae, Hearn, Medicine Hat and Wyoming cratons were all active during the Paleoproterozoic era and their interactions, particularly coeval subductions and collisions, are largely responsible for the basement geology beneath western Laurentia.

Imaging crustal roots in the Europe-Mediterranean region: a surface wave perspective

NASA Astrophysics Data System (ADS)

Villaseñor, Antonio

2016-04-01

The thickness of crustal roots is a fundamental constrain to understand the geodynamic evolution of mountain ranges. Crustal thickness can be inferred from a variety of geophysical observables (e.g. gravity anomalies, active and passive seismic methods, etc). Deep seismic sounding (DSS) using controlled sources usually provides the most accurate images of the crustal structure and thickness. However it is an expensive method, and often only used for 2D profiles. On the other hand, passive seismology experiments based on earthquakes or ambient noise have generally lower resolution, but are cheaper to conduct and can provide 3D images. As a result of the success of USArray, experiments consisting of dense deployments of broadband seismometers have become the modern standard approach for imaging continental regions. This, in combination with the densification of permanent regional monitoring networks and the use of seismic ambient noise, has allowed to use surface waves to image with increased resolution regions such as Europe and the Mediterranean basin. Surface waves are not very sensitive to the location of discontinuities such as the Moho, but can provide good constraints on the lateral variation of crustal thickness. Here, by combining continuous recordings of array experiments and permanent networks, I present a new tomographic model of surface wave velocities in the Europe-Mediterranean region that can be used as a proxy for crustal thickness. Large low velocity anomalies corresponding to thick crust are observed as expected in mountain ranges such as the Atlas, Pyrenees and Alps where crustal thickening has occurred as a result of continental collision. In addition, similarly large low velocity anomalies are observed in regions where slab roll-back/break-off has occurred (Betic-Rif, NW and SE Carpathians, Apennines, western Balkan peninsula). While these anomalies might not all be originated by thick crust, in some cases such as the Rif-western Betics previously unknown thick crust (without topographic nor gravimetric signature) has been confirmed by recent DSS studies, suggesting different a mechanism for crustal thickening than simply continental collision. This research has been funded by projects MISTERIOS (CGL2013-48601-C2-1-R) and VeTools.

Hemispheric variation of the depth dependent attenuation and velocity structures of the top half of the inner core determined from global seismic array data

NASA Astrophysics Data System (ADS)

Iritani, R.; Takeuchi, N.; Kawakatsu, H.

2012-12-01

Previous studies suggested the existence of the hemispheric heterogeneities in the top 100 km of the inner core [eg. Wen and Niu, 2002]. Although depth profiles of the attenuation and velocity of the inner core provide important clues to constrain the physical mechanism and the growing process of the inner core, they have not yet been well constrained primarily due to difficulties in analyzing core phases with phase overlapping. We have previously developed a waveform inversion method to be applicable to such complex waveforms [Iritani et al., 2010, GRL] and revealed the depth profile of the attenuation beneath North America [Iritani et al., 2011, AGU]. In this study, we applied our method to a large number of broadband seismic arrays to compare depth profiles of the top half of the inner core in various regions. The data set consists of about 8,500 traces from Japanese F-net, NECESSArray (a large temporary broadband seismic array installed in northeastern China), permanent European stations, USArray and PASSCAL arrays deployed in a number of places in the world. Regions of the inner core sampled by core phases are beneath eastern Pacific, North America and Africa in the western hemisphere (WH), and beneath eastern and central Asia in the eastern hemisphere (EH). The obtained attenuation models for the WH show the gradually increase from ICB and have a peak around a 200 km depth. In contrast, the models for the EH have a high attenuation zone at the top 150 km layer. However, almost all models show common features below a depth of 250 km where the attenuation starts to gradually decrease with depth. It appears that hemispheric heterogeneities of the inner core are confined to the top 150 - 250 km of the inner core. Velocity models obtained by using various core phase data (PKP(DF), PKP(BC), PKP(CD) and PKP(Cdiff)) will be also presented to infer the origin of hemispherical heterogeneities and their relationship to the growing process of the inner core.

Leveraging High Resolution Topography for Education and Outreach: Updates to OpenTopography to make EarthScope and Other Lidar Datasets more Prominent in Geoscience Education

NASA Astrophysics Data System (ADS)

Kleber, E.; Crosby, C. J.; Arrowsmith, R.; Robinson, S.; Haddad, D. E.

2013-12-01

The use of Light Detection and Ranging (lidar) derived topography has become an indispensable tool in Earth science research. The collection of high-resolution lidar topography from an airborne or terrestrial platform allows landscapes and landforms to be represented at sub-meter resolution and in three dimensions. In addition to its high value for scientific research, lidar derived topography has tremendous potential as a tool for Earth science education. Recent science education initiatives and a community call for access to research-level data make the time ripe to expose lidar data and derived data products as a teaching tool. High resolution topographic data fosters several Disciplinary Core Ideas (DCIs) of the Next Generation Science Standards (NGS, 2013), presents respective Big Ideas of the new community-driven Earth Science Literacy Initiative (ESLI, 2009), teaches to a number National Science Education Standards (NSES, 1996), and Benchmarks for Science Literacy (AAAS, 1993) for science education for undergraduate physical and environmental earth science classes. The spatial context of lidar data complements concepts like visualization, place-based learning, inquiry based teaching and active learning essential to teaching in the geosciences. As official host to EarthScope lidar datasets for tectonically active areas in the western United States, the NSF-funded OpenTopography facility provides user-friendly access to a wealth of data that is easily incorporated into Earth science educational materials. OpenTopography (www.opentopography.org), in collaboration with EarthScope, has developed education and outreach activities to foster teacher, student and researcher utilization of lidar data. These educational resources use lidar data coupled with free tools such as Google Earth to provide a means for students and the interested public to visualize and explore Earth's surface in an interactive manner not possible with most other remotely sensed imagery. The education section of the OpenTopography portal has recently been strengthened with the addition of several new resources and the re-organization of existing content for easy discovery. New resources include a detailed frequently asked questions (FAQ) section, updated 'How-to' videos for downloading data from OpenTopography and additional webpages aimed at students, educators and researchers leveraging existing and updated resources from OpenTopography, EarthScope and other organizations. In addition, the OpenLandform catalog, an online collection of classic geologic landforms depicted in lidar, has been updated to include additional tectonic landforms from EarthScope lidar datasets.

PBO Nucleus Project Status: Integration of 209 Existing GPS Stations into the Plate Boundary Observatory

NASA Astrophysics Data System (ADS)

Blume, F.; Meertens, C.; Anderson, G.; Eriksson, S.; Boyce, E.

2007-12-01

Tectonic and earthquake research in the US has experienced a quiet revolution over the last decade precipitated by the recognition that slow-motion faulting events can both trigger and be triggered by regular earthquakes. Transient motion has now been found in essentially all tectonic environments, and the detection and analysis of such events is the first-order science target of the EarthScope Project. Because of this and a host of other fundamental tectonics questions that can be answered only with long-duration geodetic time series, the incipient 1100-station EarthScope Plate Boundary Observatory (PBO) network has been designed to leverage 445 existing continuous GPS stations whose measurements extend back over a decade. The irreplaceable recording history of these stations will accelerate EarthScope scientific return by providing the highest possible resolution. This resolution will be used to detect and understand transients, to determine the three-dimensional velocity field (particularly vertical motion), and to improve measurement precision by understanding the complex noise sources inherent in GPS. The PBO Nucleus project supports the operation, maintenance and hardware upgrades of a subset of the six western U.S. geodetic networks until they are subsumed by PBO. Uninterrupted data flow from these stations will effectively double the time-series length of PBO over the expected life of EarthScope, and has created, for the first time, a single GPS-based geodetic network in the US. The other existing sites remain in operation under support from non-NSF sources (e.g. the USGS), and EarthScope continues to benefit from their continued operation On the grounds of relevance to EarthScope science goals, geographic distribution and data quality, 209 of the 432 existing stations were selected as the nucleus upon which to build PBO. Conversion of these stations to a PBO-compatible mode of operation was begun under previous funding, and as a result data now flow directly to PBO archives and processing centers while maintenance, operations, and meta-data requirements are continue to be upgraded to PBO standards. At the end of this project all 209 stations will be fully incorporated into PBO, meeting all standards for new PBO construction including data communications and land use permits. Funds for operation of these stations have been included in planned budgets for PBO after the construction phase ends and PBO begins an operational phase in 2008. At this time work on the project is apporixmately 80% complete, with over 90% of the stations having been upgraded. The data from these stations serve a much larger audience than just the few people who work to keep them operating. This project is now collecting the data that will be used by the next generation of solid-earth researchers for at least two decades. Educational modules are being developed by a team of researchers, educators, and curriculum development professionals, and are being disseminated through regional and national workshops. An interactive website provides the newest developments in tectonics research to K-16 classrooms.

The Salton Seismic Imaging Project: Tomographic characterization of a sediment-filled rift valley and adjacent ranges, southern California

NASA Astrophysics Data System (ADS)

Davenport, K.; Hole, J. A.; Stock, J. M.; Fuis, G. S.; Carrick, E.; Tikoff, B.

2011-12-01

The Salton Trough in Southern California represents the northernmost rift of the Gulf of California extensional system. Relative motion between the Pacific and North American plates is accommodated by continental rifting in step-over zones between the San Andreas, Imperial, and Cerro Prieto transform faults. Rapid sedimentation from the Colorado River has isolated the trough from the southern portion of the Gulf of California, progressively filling the subsiding rift basin. Based on data from previous seismic surveys, the pre-existing continent has ruptured completely, and a new ~22 km thick crust has been created entirely by sedimentation overlying rift-related magmatism. The MARGINS, EarthScope, and USGS-funded Salton Seismic Imaging Project (SSIP) was designed to investigate the nature of this new crust, the ongoing process of continental rifting, and associated earthquake hazards. SSIP, acquired in March 2011, comprises 7 lines of onshore seismic refraction / wide-angle reflection data, 2 lines of refraction / reflection data in the Salton Sea, and a line of broadband stations. This presentation focuses on the refraction / wide-angle reflection line across the Imperial Valley, extending ~220 km across California from Otay Mesa, near Tijuana, to the Colorado River. The data from this line includes seventeen 100-160 kg explosive shots and receivers at 100 m spacing across the Imperial Valley to constrain the structure of the Salton Trough rift basin, including the Imperial Fault. Eight larger shots (600-920 kg) at 20-35 km spacing and receivers at 200-500 m spacing extend the line across the Peninsular Ranges and the Chocolate Mountains. These data will contrast the structure of the rift to that of the surrounding crust and provide constraints on whole-crust and uppermost mantle structure. Preliminary work has included tomographic inversion of first-arrival travel times across the Valley, emphasizing a minimum-structure approach to create a velocity model of the upper crust. Ongoing modeling provides constraints on the basin margins, showing a steeply dipping western edge of the rift valley approximately coincident to the shoreline of the ancient Lake Cahuilla. Low velocity sediments and low velocity crystalline crust within the Imperial Valley are consistent with previous studies and contrast with faster crystalline rocks near the surface outside the rift. Ongoing analysis will provide a more detailed image of upper crustal structure, as well as preliminary modeling of the entire crust.

Synthesis of Creep Measurements from Strainmeters and Creepmeters along the San Andreas Fault: Implications for Seismic vs. Aseismic Partitioning

NASA Astrophysics Data System (ADS)

Mencin, D.; Gottlieb, M. H.; Hodgkinson, K. M.; Bilham, R. G.; Mattioli, G. S.; Johnson, W.; Van Boskirk, E.; Meertens, C. M.

2015-12-01

Strainmeters and creepmeters have been operated along the San Andreas Fault, observing creep events for decades. In particular, the EarthScope Plate Boundary Observatory (PBO) has added a significant number of borehole strainmeters along the San Andreas Fault (SAF) over the last decade. The geodetic data cover a significant temporal portion of the inferred earthquake cycle along this portion of the SAF. Creepmeters measure the surface displacement over time (creep) with short apertures and have the ability to capture slow slip, coseismic rupture, and afterslip. Modern creepmeters deployed by the authors have a resolution of 5 µm over a range of 10 mm and a dynamic sensor with a resolution 25 µm over a range 2.2 m. Borehole strainmeters measure local deformation some distance from the fault with a broader aperture. Borehole tensor strainmeters principally deployed as part of the PBO, measure the horizontal strain tensor at a depth of 100-200 m with a resolution of 10-11 strain and are located 4 - 10 km from the fault with the ability to image a 1 mm creep event acting on an area of ~500 m2 from over 4 km away (fault perpendicular). A single borehole tensor strainmeter is capable of providing broad constraints on the creep event asperity size, location, direction and depth of a single creep event. The synthesis of these data from all the available geodetic instruments proximal to the SAF presents a unique opportunity to constrain the partitioning between aseismic and seismic slip on the central SAF. We show that simple elastic half-space models allow us to loosely constrain the location and depth of any individual creep event on the fault, even with a single instrument, and to image the accumulation of creep with time.

Lithospheric Structure and Dynamics: Insights Facilitated by the IRIS/PASSCAL Facility

NASA Astrophysics Data System (ADS)

Meltzer, A.

2002-12-01

Through the development of community-based facilities in portable array seismology, a wide-range of seismic methods are now standard tools for imaging the Earth's interior, extending geologic observations made at the surface to depth. The IRIS/PASSCAL program provides the seismological community with the ability to routinely field experimental programs, from high-resolution seismic reflection profiling of the near surface to lithospheric scale imaging with both active and passive source arrays, to understand the tectonic evolution of continents, how they are assembled, disassembled, and modified through time. As our ability to record and process large volumes of data has improved we have moved from simple 1-D velocity models and 2-D structural cross sections of the subsurface to 3-D and 4-D images to correlate complex surface tectonics to processes in the Earth's interior. Data from individual IRIS/PASSCAL experiments has fostered multidisciplinary studies, bringing together geologists, geochemists, and geophysicists to work together on common problems. As data is collected from a variety of tectonic environments around the globe common elements begin to emerge. We now recognize and study the inherent lateral and vertical heterogeneity in the crust and mantle lithosphere and its role in controlling deformation, the importance of low velocity mobile mantle in supporting topography, and the importance of fluids and fluid migration in magmatic and deformational processes. We can image and map faults, fault zones, and fault networks to study them as systems rather than isolated planes of deformation to better understand earthquake nucleation, rupture, and propagation. An additional benefit of these community-based facilities is the pooling of resources to develop effective and sustainable education and outreach programs. These programs attract new students to pursue careers in earth science, engage the general public in the scientific enterprise, raise the profile of the earth sciences, and reveal the importance of earth processes in shaping the environment in which we live. Future challenges facing our community include continued evolution of existing facilities to keep pace with scientific inquiry, routinely utilizing fully 3-D and where appropriate 4-D data sets to understand earth structure and dynamics, and the manipulation, and analysis of large multidisciplinary data sets. Community models should be considered as a mechanism to integrate, analyze, and share data and results within a process oriented framework. Exciting developments on the horizon include EarthScope. To maximize the potential for significant advances in our understanding of tectonic processes, observations from new EarthScope facilities must be integrated with additional geologic data sets of similar quality and resolution. New real-time data streams combined with new data integration, analysis, and visualization tools will provide us with the ability to integrate data across a continuous range of spatial scales providing a new and coherent view of lithospheric dynamics from local to plate scale.

Imaging lithosphere structures using long period surface waves from ambient noise: a case study in western USA

NASA Astrophysics Data System (ADS)

Yang, Y.

2013-12-01

Since the emerging of ambient noise tomography in 2005, it has become a well-established method and been applied all over the world to imaging crustal and uppermost mantle structures because of its exclusive capability to extract short period surface waves. Most studies of ambient noise tomography performed so far use surface waves at periods shorter than 40/50 sec. There are a few studies of long period surface wave tomography from ambient noise (longer than 50 sec) in continental and global scales. To our knowledge, almost no tomography studies have been performed using long period surface waves (~50-200 sec) from ambient noise in regional scales with an aperture of several hundred kilometres. In this study, we demonstrate the capability of using long period surface waves from ambient noise in regional surface wave tomography by showing a case study of western USA using the USArray Transportable component (TA). We select about 150 TA stations located in a region including northern California, northern Nevada and Oregon as the 'base' stations and about 200 stations from Global Seismographic Network (GSN) and The International Federation of Digital Seismograph Networks (FDSN) as the 'remote' stations. We perform monthly cross-correlations of continuous ambient noise data recorded in 2006-2008 between the 'base' stations and the 'remote' stations and then use a stacking method based on instantaneous phase coherence to stack the monthly cross-correlations to obtain the final cross-correlations. The results show that high signal-to-noise ratio long period Raleigh waves are obtained between the 'base' stations and 'remote' stations located several thousand or even more than ten thousand kilometres away from the 'base' stations. By treating each of the 'remote' station as a 'virtual' teleseismic earthquake and measuring surface wave phases at the 'base' stations, we generate phase velocity maps at 50-200 sec periods in the regions covered by the 'base' stations using an array-based two-plane-wave tomography method. To evaluate the reliability of the resulting phase velocity maps, we compare them with published phase velocity maps using the same tomography method but based on teleseismic data. The comparison shows that long period surface wave phase velocity maps based 'virtual' events from ambient noise and those based on natural earthquakes are very similar with differences within the range of uncertainties. The similarity of phase velocity maps justifies the application of long period surface waves from ambient noise in regional lithosphere imaging. The successful extraction of long period surface waves between station pairs with distances as long as several thousand or ten thousand kilometres can link seismic arrays located in different continents, such as CEArray in China and USArray in USA. With the rapid developments of large scale seismic arrays in different continents, those inter-continental surface waves from ambient noise can be incorporated in both regional- and global-scale surface wave tomography to significantly increase the path coverage in both lateral and azimuthal senses, which is essential to improving imaging of high resolution heterogeneities and azimuthal anisotropy, especially at regions with gaps of azimuthal distributions of earthquakes.

Mermaid floating seismometer : A versatile Oceanographic profiler dedicated to the Earthscope Ocean Program.

NASA Astrophysics Data System (ADS)

Hello, Y.; Nolet, G.; Bonnieux, S.; Yegikyan, M.; Chao, Y.; Chen, J.

2016-12-01

Mermaids have been developed to improve seismic data coverage in the oceanic domain for imaging of the Earth's interior. The first generation of Mermaids was housed in conventional Argo-type floats, while hardware and software was developed to analyze acoustic signals, determine whether an earthquake has been recorded, and whether the Mermaid should to come up to the surface and transmit to the satellite. Since 2012, we have deployed small test networks of Mermaids in the Indian Ocean, and in the Mediterranean sea, and we present at this meeting the result from a main network of 9 Mermaids deployed since mid 2014 in the Galapagos archipelago to image the deep plume structure. Since then, we have moved from typical cylinder container, which equips most of the Argo Floats, to a more suitable spherical design, which allows for a larger power supply and more versatile payload. The life time of the new Mermaids is 6 years if sampling continuously for seismic signals, e.g. for seismic tomography by providing worldwide coverage of P wave arrival times. The passband can be widened to allow for monitoring of whale and dolphin sounds. An interface board allows to connect up to 8 external sensors to serve other goals (bio-Argo, geochemical, meteorological). This year we have started collaboration with Sea-Trec to equip the Mermaids with an optional new green renewable power source to guaranty its 6 years lifetime even with a full payload. The Mermaids monitor continuously during the parking phase when drifting freely at a depth down to 3000m, but also provide Argo profiles during the descent. We are collaborating with Sea-Bird to customize an SBE37 to equip the Mermaid for salinity measurements. The new Mermaid has all the features to answer many scientific goals, and a project to develop a user-friendly, adaptable, software system has begun in collaboration with i3s. The first stage of a global network, EarthScope-Oceans, will be launched in 2017, and is planned to grow to 500 units to image the deep interior of the Earth.

Full-waveform Inversion for Localized 3-D S-velocity Structure in D" Beneath the Caribbean using US-Array Data

NASA Astrophysics Data System (ADS)

Borgeaud, A. F. E.; Konishi, K.; Kawai, K.; Geller, R. J.

2015-12-01

The region beneath Central America is known to have significant lateral velocity heterogeneities from the upper mantle down to the lowermost mantle. It is also known for its long history of subducting oceanic plates and fragmented plate remnants that sunk to the lowermost mantle (e.g., Ren et al., 2007). In this study, we use localized full-waveform inversion to invert for the 3-D S-velocity beneath the Caribbean. We use the DSM (Kawai et al., 2006) to compute 1-D synthetic seismograms and the first-order Born approximation to compute the partial derivatives for 3-D structure. We use a larger dataset with better coverage than Kawai et al. (2014), consisting of S and ScS phases from US-Array data for events in South America. The resulting 3-D model can contribute to understanding whether the cause of the velocity anomalies is thermal, chemical, or due to phase transitions.

No fault of their own: Increasing public awareness of earthquakes in aseismic regions

NASA Astrophysics Data System (ADS)

Galvin, J. L.; Pickering, R. A.; Wetzel, L. R.

2011-12-01

EarthScope's Transportable Array (TA) project is installing seismographs across the US, progressing from North America's seismically active West Coast to the passive Atlantic margin. The array consists of 400 seismic stations spaced ~70 km apart for a continental-scale experiment lasting 15 years. A student/faculty team from Eckerd College participated by using computer-based tools to identify potential seismograph sites; conducting field investigations to confirm site suitability; initiating contact with landowners; and preparing reconnaissance reports for future earthquake recording stations in Florida. An ideal seismograph site is in a quiet, dry, unshaded, open area that is remote yet accessible, with cellular network coverage and a willing private landowner. Scouting for site locations presented many challenges, including land use and ownership patterns; low-lying, flooded topography; noisy Atlantic and Gulf coastal regions; extensive river and lake systems; environmentally protected areas; road patterns with high traffic; urban population centers; and a populace unfamiliar with earthquakes. While many of these factors were unavoidable, developing the public's interest in seismology was a crucial step in gaining landowner participation. The majority of those approached were unfamiliar with the importance of earthquake research in an aseismic location. Being presented with this challenge encouraged the team to formulate different approaches to promote public interest and understanding of earthquake research in locations indirectly affected by seismic activity. Throughout the project, landowners expressed greater interest or were more likely to participate for a variety of reasons. For instance, landowners that had personal experience with earthquakes, were involved with the scientific community, or had previously collaborated with other research projects were most receptive to participating in the TA program. From this observation, it became clear that relating potential site hosts to earthquake events or the scientific research process was beneficial for gaining citizen support. For example, many landowners expressed interest in seismic research if they or their family members had experienced an earthquake. For residents lacking a personal association with earthquakes or science in general, it was important to explain why recording earthquakes in a seismically inactive area could be beneficial. For instance, explaining that data collected from the TA project could aid in research of other events including hurricanes and sink holes made the program seem more pertinent to Florida citizens. After spending the summer in contact with Florida residents, the team established that the most effective route to cultivate public interest in seismology was to make the study's purpose applicable to their everyday lives. In doing so, citizens felt directly connected to the project, and were therefore more enthusiastic to participate and become educated on the topic of seismology.

Lithospheric Delamination or Relict Slab Beneath the Former North American Cratonic Margin in Idaho and Oregon? New Constraints From Seismic Tomography.

NASA Astrophysics Data System (ADS)

Stanciu, A. C.; Russo, R. M.; Mocanu, V. I.; VanDecar, J. C.; Hongsresawat, S.; Bremner, P. M.; Torpey, M. E.; Panning, M. P.

2016-12-01

We present a new high-resolution P-wave velocity model of the upper mantle beneath the former passive margin of the North American craton in Oregon and Idaho. We identify high velocity anomalies in the central part of the model and low velocity anomalies to the northwest and southeast. Our results derive from an integrated data set of teleseismic P waves recorded at 145 broadband stations, 85 deployed between 2011 and 2013 as part of the IDOR Passive experiment, and 60 USArray-TA stations. We determined 15,000 travel-times using multi-channel cross-correlation (VanDecar and Crosson, 1990). Phanerozoic tectonic events that affected upper mantle seismic structure here include subduction of Farallon and Juan de Fuca lithosphere, accretion of Blue Mountains terranes, Sevier and Laramide orogenies, Idaho batholith formation, Yellowstone and Columbia River volcanism, and Basin and Range extension. Our results indicate a high P-wave velocity anomaly located beneath the Idaho Batholith in west-central Idaho traceable down to 150-200 km depth. A similar anomaly identified by Schmandt and Humphrey (2011) beneath Washington and Montana was interpreted as a slab remnant from the accretion of Siletzia to North America. Alternatively, the fast Vp anomalies are delaminated North American craton lithosphere. Thickened lithosphere may have formed during Farallon subduction, terrane collision and accretion. Crust as much as 55 km thick present during Late Cretaceous (Foster et al., 2001; Gaschnig et al., 2011) is potentially indicative of lithospheric thickening leading to delamination. To the southeast, upper mantle low velocity anomalies occur beneath the Western Snake River Plain. We associate these low velocities with high temperatures generated by the Yellowstone mantle plume system. We observe a low velocity anomaly beneath the Wallowa Mountains starting at 150-200 km extending to depths below the resolution of our model.

The 2008 Wells, Nevada Earthquake Sequence: Application of Subspace Detection and Multiple Event Relocation Techniques

NASA Astrophysics Data System (ADS)

Nealy, J. L.; Benz, H.; Hayes, G. P.; Bergman, E.; Barnhart, W. D.

2016-12-01

On February 21, 2008 at 14:16:02 (UTC), Wells, Nevada experienced a Mw 6.0 earthquake, the largest earthquake in the state within the past 50 years. Here, we re-analyze in detail the spatiotemporal variations of the foreshock and aftershock sequence and compare the distribution of seismicity to a recent slip model based on inversion of InSAR observations. A catalog of earthquakes for the time period of February 1, 2008 through August 31, 2008 was derived from a combination of arrival time picks using a kurtosis detector (primarily P arrival times), subspace detector (primarily S arrival times), associating the combined pick dataset, and applying multiple event relocation techniques using the 19 closest USArray Transportable Array stations, permanent regional seismic monitoring stations in Nevada and Utah, and temporary stations deployed for an aftershock study. We were able to detect several thousand earthquakes in the months following the mainshock as well as several foreshocks in the days leading up to the event. We reviewed the picks for the largest 986 earthquakes and relocated them using the Hypocentroidal Decomposition (HD) method. The HD technique provides both relative locations for the individual earthquakes and an absolute location for the earthquake cluster, resulting in absolute locations of the events in the cluster having minimal bias from unknown Earth structure. A subset of these "calibrated" earthquake locations that spanned the duration of the sequence and had small uncertainties in location were used as prior constraints within a second relocation effort using the entire dataset and the Bayesloc approach. Accurate locations (to within 2 km) were obtained using Bayesloc for 1,952 of the 2,157 events associated over the seven-month period of the study. The final catalog of earthquake hypocenters indicates that the aftershocks extend for about 20 km along the strike of the ruptured fault. The aftershocks occur primarily updip and along the southwestern edge of the zone of maximum slip as modeled by seismic waveform inversion (Dreger et al., 2011) and by InSAR. The aftershock locations illuminate areas of post-mainshock strain increase and their depths are consistent with InSAR imaging, which showed that the Wells earthquake was a buried source with no observable near-surface offset.

CyberTEAM Interactive Epicenter Locator Tool

NASA Astrophysics Data System (ADS)

Ouyang, Y.; Hayden, K.; Lehmann, M.; Kilb, D.

2008-12-01

News coverage showing collapsed buildings, broken bridges and smashed cars help middle school students visualize the hazardous nature of earthquakes. However, few students understand how scientists investigate earthquakes through analysis of data collected using technology devices from around the world. The important findings by Muawia Barazangi and James Dorman in 1969 revealed how earthquakes charted between 1961 and 1967 delineated narrow belts of seismicity. This important discovery prompted additional research that eventually led to the theory of plate tectonics. When a large earthquake occurs, people from distances near and far can feel it to varying degrees. But how do scientists examine data to identify the locations of earthquake epicenters? The scientific definition of an earthquake: "a movement within the Earth's crust or mantle, caused by the sudden rupture or repositioning of underground material as they release stress" can be confusing for students first studying Earth science in 6th grade. Students struggle with understanding how scientists can tell when and where a rupture occurs, when the inner crust and mantle are not visible to us. Our CyberTEAM project provides 6th grade teachers with the opportunity to engage adolescents in activities that make textbooks come alive as students manipulate the same data that today's scientists use. We have developed an Earthquake Epicenter Location Tool that includes two Flash-based interactive learning objects that can be used to study basic seismology concepts and lets the user determine earthquake epicenters from current data. Through the Wilber II system maintained at the IRIS (Incorporated Research Institutions for Seismology) Web site, this project retrieves seismic data of recent earthquakes and makes them available to the public. Students choose an earthquake to perform further explorations. For each earthquake, a selection of USArray seismic stations are marked on a Google Map. Picking a station on the map, students are presented with the seismogram recorded at that station and they use a slide tool to mark the P- and S-waves. Allowing reasonable errors, the Web-based Earthquake Epicenter Location Tool compares the students' markings with the true data. Students are awarded with a certificate when the results match. The Earthquake Epicenter Location Tool presents an innovative approach to integrate Cyberinfrastructure (CI) in middle school classrooms by providing students with an easy to use interface to access CI data.

Thermal classification of lithospheric discontinuities beneath USArray

NASA Astrophysics Data System (ADS)

Hansen, Steven M.; Dueker, Ken; Schmandt, Brandon

2015-12-01

Broadband seismic data from the United States were processed into Ps and Sp receiver function image volumes for the purpose of constraining negative velocity gradients (NVG) at depths between the Moho and 200 km. Moho depth picks from the two independent datasets are in good agreement, however, large discrepancies in NVG picks occur and are attributed to free-surface multiples which obscure deep NVG arrivals in the Ps data. From the Sp data, shallow NVG are found west of the Rockies and in the central US while deep and sporadic NVG are observed beneath the Great Plains and northern Rockies. To aid the interpretation of the observed NVG arrivals, the mantle thermal field is estimated by mapping surface wave tomography velocities to temperature assuming an anelastic olivine model. The distribution of temperature versus NVG depth is bi-modal and displays two distinct thermal populations that are interpreted to represent both the lithosphere-asthenosphere boundary (LAB) and mid-lithosphere discontinuities (MLD). LAB arrivals occur in the western US at 60-85 km and 1200-1400 °C depth suggesting that they manifest partial melt near the base of the thermal plate. MLD arrivals primarily occur at 70-110 km depth and 700-900 °C and we hypothesize that these arrivals are caused by a low-velocity metasomatic layer containing phlogopite resulting from magma crystallization products that accumulate within long-lived thick lithosphere.

Radial anisotropy of the North American upper mantle based on adjoint tomography with USArray

NASA Astrophysics Data System (ADS)

Zhu, Hejun; Komatitsch, Dimitri; Tromp, Jeroen

2017-10-01

We use seismic data from USArray to image the upper mantle underneath the United States based on a so-called `adjoint tomography', an iterative full waveform inversion technique. The inversion uses data from 180 regional earthquakes recorded by 4516 seismographic stations, resulting in 586 185 frequency-dependent measurements. Three-component short-period body waves and long-period surface waves are combined to simultaneously constrain deep and shallow structures. The transversely isotropic model US22 is the result of 22 pre-conditioned conjugate-gradient iterations. Approximate Hessian maps and point-spread function tests demonstrate good illumination of the study region and limited trade-offs among different model parameters. We observe a distinct wave-speed contrast between the stable eastern US and the tectonically active western US. This boundary is well correlated with the Rocky Mountain Front. Stable cratonic regions are characterized by fast anomalies down to 250-300 km, reflecting the thickness of the North American lithosphere. Several fast anomalies are observed beneath the North American lithosphere, suggesting the possibility of lithospheric delamination. Slow wave-speed channels are imaged beneath the lithosphere, which might indicate weak asthenosphere. Beneath the mantle transition zone of the central US, an elongated north-south fast anomaly is observed, which might be the ancient subducted Farallon slab. The tectonically active western US is dominated by prominent slow anomalies with magnitudes greater than -6 per cent down to approximately 250 km. No continuous lower to upper mantle upwellings are observed beneath Yellowstone. In addition, our results confirm previously observed differences between oceans and continents in the anisotropic parameter ξ = (βh/βv)2. A slow wave-speed channel with ξ > 1 is imaged beneath the eastern Pacific at depths from 100 to 200 km, reflecting horizontal shear within the asthenosphere. Underneath continental areas, regions with ξ > 1 are imaged at shallower depths around 100 km. They are characterized by fast shear wave speeds, suggesting different origins of anisotropy underneath oceans and continents. The wave speed and anisotropic signatures of the western Atlantic are similar to continental areas in comparison with the eastern Pacific. Furthermore, we observe regions with ξ < 1 beneath the tectonically active western US at depths between 300 and 400 km, which might reflect vertical flows induced by subduction of the Farallon and Juan de Fuca Plates. Comparing US22 with several previous tomographic models, we observe relatively good correlations for long-wavelength features. However, there are still large discrepancies for small-scale features.

Inversion of magnetotelluric data using integral equation approach with variable sensitivity domain: Application to EarthScope MT data

NASA Astrophysics Data System (ADS)

Čuma, Martin; Gribenko, Alexander; Zhdanov, Michael S.

2017-09-01

We have developed a multi-level parallel magnetotelluric (MT) integral equation based inversion program which uses variable sensitivity domain. The limited sensitivity of the data, which decreases with increasing frequency, is exploited by a receiver sensitivity domain, which also varies with frequency. We assess the effect of inverting principal impedances, full impedance tensor, and full tensor jointly with magnetovariational data (tipper). We first apply this method to several models and then invert the EarthScope MT data. We recover well the prominent features in the area including resistive structure associated with the Juan de Fuca slab subducting beneath the northwestern United States, the conductive zone of partially melted material above the subducting slab at the Cascade volcanic arc, conductive features in the Great Basin and in the area of Yellowstone associated with the hot spot, and resistive areas to the east corresponding to the older and more stable cratons.

Professional Development for Researchers in Solid Earth Science Evolved to Include Scientific and Educational Content

NASA Astrophysics Data System (ADS)

Eriksson, S. C.; Arrowsmith, R.; Olds, S. E.

2011-12-01

Integrated measures of crustal deformation provide valuable insight about tectonic and human-induced processes for scientists and educators alike. UNAVCO in conjunction with EarthScope initiated a series of short courses for researchers to learn the processing and interpretation of data from new technologies such as high precision GPS, Strainmeter, InSar and LiDAR that provide deformation information relevant to many geoscience sub-disciplines. Intensive short courses of a few days and the widespread availability of processed data through large projects such as EarthScope and GEON enable more geoscientists to incorporate these data into diverse projects. Characteristics of the UNAVCO Short Course Series, reaching over 400 participants since 2005, include having short course faculty who have pioneered development of each technology; open web-access to course materials; processing software installed on class-ready computers; no course fees; scholarships for students, post-doctoral fellows, and emerging faculty when needed; formative evaluation of the courses; community-based decisions on topics; and recruitment of participants across relevant geoscience disciplines. In 2009, when EarthScope airborne LiDAR data became available to the public through OpenTopographhy, teaching materials were provided to these researchers to incorporate the latest technologies into teaching. Multiple data sets across technologies have been developed with instructions on how to access the various data sets and incorporate them into geological problem sets. Courses in GPS, airborne LiDAR, strainmeter, and InSAR concentrate on data processing with examples of various geoscience applications. Ground-based LiDAR courses also include data acquisition. Google Earth is used to integrate various forms of data in educational applications. Various types of EarthScope data can now be used by a variety of geoscientists, and the number of scientists who have the skills and tools to use these various datasets has increased. Evaluation data show that participants highly value these courses and are interested in distance learning; however, due to the hands-on nature of processing data and the one-on-one teaching commonly used in these courses, distance learning has been minimal. The diversity of participants is high for the geosciences. The courses also play an important role in increasing the scientific capacity in the international community.

Inheritance vs ongoing evolution of the passive margin lithosphere in the southeastern United States: A comparison of <50Ma tectonism with tomographically imaged lithospheric structures.

NASA Astrophysics Data System (ADS)

Wagner, L. S.; Fischer, K. M.; Hawman, R. B.; Hopper, E.; Howell, D.

2017-12-01

The southeastern United States is an archetypical passive margin, and yet significant evidence exists that this region, separated from the nearest plate boundary by thousands of kilometers and over 170 Ma, has experienced significant tectonism since the Eocene. This tectonism includes volcanism, uplift/deformation, and ongoing seismicity such as the 2011 Mw = 5.8 Mineral, VA earthquake and the 1886 M=7 Charleston, SC event. For each of these examples, numerous theories exist on their respective causes. However, there are two common themes that span all of these types of events: first, their proximity to regional terrane boundaries whose inherited structures could play a role; second, the nature of the mantle lithosphere underlying them. We present a recently completed inversion of seismic Rayleigh waves for the shear wave velocity structure of the uppermost 150 - 200 km beneath the southeastern United States. This inversion includes not only EarthScope Transportable Array data, but also the data from the 85 broadband stations installed as part of the Flex Array SouthEastern Suture of the Appalachian Mountains Experiment (SESAME). We find some evidence for structures inherited from previous episodes of rifting, accretion, and orogenesis. However, we also find several examples of mantle lithospheric structures that spatially correlate strongly with Eocene to recent tectonic activity, but do not correlate to any known inherited geometries. These examples include a small but pronounced sub-crustal low velocity anomaly beneath the Eocene volcanoes in western Virginia and eastern West Virginia, as well as evidence for mantle delamination beneath the Cape Fear Arch and uplifted portions of the Orangeburg Escarpment. We will discuss these, along with instances of recent tectonism in our study area that do not bear any obvious relationship to lithospheric structures, in order to shed light on the causes of ongoing tectonic activity in this supposedly "passive" margin setting.

Lithospheric buckling and far-foreland deformation during the Laramide and Appalachian orogenies

NASA Astrophysics Data System (ADS)

Tikoff, B.; Siddoway, C. S.

2017-12-01

Major intraplate tectonics within North America (Laurentia) occurs during times of major orogenesis along the plate margins. During mountain building, typical structures of the hinterland are an orogenic plateau and fold-and-thrust belts, while in the far foreland (intraplate) areas long-wavelength ( 200 km or longer) folds and fault-reactivation features form. Long-wavelength folds are evident in both the Appalachian and Laramide orogenic forelands, with the stratigraphy recording the timing of the uplift. This contribution examines the model of lithospheric buckling - periodic folding associated with a horizontal endload on the edge of the plate - based on scaled, physical experiments and corroborated by numerical models. The Laramide (75-55 Ma) intraplate orogen in the classical location in Wyoming contains basement-cored arches spaced 200 km apart, for which the mechanism of uplift is questioned. Seismic evidence obtained for the Bighorn uplift, Wyoming, obtained by the EarthScope Bighorn project, shows an upwarp of the Moho beneath, but oblique to the trend of the surface exposure of the basement arch. Both the surface and Moho exhibit approximately the same structural relief. The seismic data exhibit no evidence for a regionally continuous decollement, nor is there evidence of rotation of structural markers within these features, of the type that is observed in the detached fold-and-thrust belt. The intraplate region affected by long-wavelength folding includes western Wyoming, with continuation of some features across the E-W-oriented Cheyenne belt (e.g., Rock Springs-Douglas Creek arch), Colorado Plateau, and High Plains east of the Rocky Mountains, where surface and subsurface structures display a series of anticlinal arches ("plains-type" folds). Appalachian mountain building also caused long-wavelength folding, with a spacing consistent with lithospheric buckling, mostly associated with the Devonian Acadian orogeny. The Laramide arches in the High Plains seem to occur on arches inherited from the Appalachian orogeny, suggesting the permanence of these lithospheric buckles once they have formed.

Along-Strike Electrical Conductivity Variations in the Incoming Plate and Shallow Forearc of the Cascadia Subduction Zone

NASA Astrophysics Data System (ADS)

Key, K.; Bedrosian, P.; Egbert, G. D.; Livelybrooks, D.; Parris, B. A.; Schultz, A.

2015-12-01

The Magnetotelluric Observations of Cascadia using a Huge Array (MOCHA) experiment was carried out to study the nature of the seismogenic locked zone and the down-dip transition zone where episodic tremor and slip (ETS) originates. This amphibious magnetotelluric (MT) data set consists of 8 offshore and 15 onshore profiles crossing from just seaward of the trench to the western front of the Cascades, with a north-south extent spanning from central Oregon to central Washington. The 71 offshore stations and the 75 onshore stations (red triangles in the image below) fit into the broader context of the more sparsely sampled EarthScope MT transportable array (black triangles) and other previous and pending MT surveys (other symbols). These data allows us to image variations in electrical conductivity along distinct segments of the Cascadia subduction zone defined by ETS recurrence intervals. Since bulk conductivity in this setting depends primarily on porosity, fluid content and temperature, the conductivity images created from the MOCHA data offer unique insights on fluid processes in the crust and mantle, and how the distribution of fluid along the plate interface relates to observed variations in ETS behavior. This abstract explores the across- and along-strike variations in the incoming plate and the shallow offshore forearc. In particular we examine how conductivity variations, and the inferred fluid content and porosity variations, are related to tectonic segmentation, seismicity and deformation patterns, and arc magma variations along-strike. Porosity inferred in the forearc crust can be interpreted in conjunction with active and passive seismic imaging results and may provide new insights on the origin of recently observed extremely high heat flow values. A companion abstract (Parris et al.) examines the deeper conductivity structure of the locked and ETS zones along the plate interface in order to identify correlations between ETS occurrence rates and inferred fluid concentrations.

Uplifting the Stable Crust of the Colorado Plateau through Crustal Hydration and Warming

NASA Astrophysics Data System (ADS)

Porter, R. C.; Holt, W. E.

2016-12-01

The Colorado Plateau (CP) is a high ( 2 km above sea level), low-relief, orogenic plateau located within the interior of the southwestern United States that presents several outstanding geologic questions, most notably about the timing and mechanism(s) for uplift. The CP was located below sea level during the Cretaceous and was uplifted to its modern elevation with little crustal shortening, making the cause of uplift enigmatic. Numerous mechanisms have been hypothesized to explain the uplift of this stable block and include delamination, mantle heating/phase changes, mantle convection, volatile addition, and various combinations of these. In order to better understand the crustal contribution to uplift, we utilize data from the EarthScope Transportable Array network to image the CP lithosphere and inform thermodynamic models of CP lower crustal composition. Rayleigh wave phase velocities calculated using ambient noise tomography and surface wave gradiometry were inverted for shear velocity resulting in a high-resolution velocity model of the CP crust and upper mantle. In order to provide greater context to these results, the thermodynamic modeling code Perple_X was utilized to forward model crustal densities, seismic velocities, and water content based on psuedosections calculated using published major element chemistry. Our seismic and modeling results show that uplift of the plateau is partially driven by hydration and extension of the lower crust, both of which reduce its density. Hydration of the CP crust likely occurred due to dewatering of the Farallon slab during flat-slab subduction and reduced lower crustal density by 70 kg/m3. Warming and extension further reduced the lower crustal density by 90 kg/m3 at the CP margins. Though these processes played a role in the uplift of the CP, additional mechanisms, likely due to mantle processes, are required to fully explain its high elevation. Additionally, hydration and subsequent dehydration may play an important role in the recent encroachment of deformation and volcanism into the interior of the CP.

Orientations and Relative Shear-strain Response Coefficients for PBO Gladwin Tensor Strainmeters from Teleseismic Love Waves

NASA Astrophysics Data System (ADS)

Roeloffs, E. A.

2016-12-01

A Gladwin Tensor Strainmeter (GTSM) is designed to measure changes of the horizontal strain tensor, derived as linear combinations of radial elongations or contractions of the strainmeter's cylindrical housing measured at four azimuths. Each radial measurement responds to changes in the areal, horizontal shear and vertical components of the strain tensor in the surrounding formation. The elastic response coefficients to these components depend on the relative elastic moduli of the housing, formation, and cement. These coefficients must be inferred for each strainmeter after it is cemented into its borehole by analyzing the instrument response to well-characterized strain signals such as earth tides. For some GTSMs of the Earthscope Plate Boundary Observatory (PBO), however, reconciling observed earth-tide signals with modeled tidal strains requires response coefficients that differ substantially between the instrument's four gauges, and/or orientation corrections of tens of degrees. GTSM response coefficients can also be estimated from high-resolution records of teleseismic Love waves from great earthquakes around the world. Such records can be used in conjunction with apparent propagation azimuths from nearby broadband seismic stations to determine the GTSM's orientation. Knowing the orientation allows the ratios between the shear strain response coefficients of a GTSM's four gauges to be estimated. Applying this analysis to 14 PBO GTSMs confirms that orientations of some instruments differ significantly from orientations measured during installation. Orientations inferred from earth-tide response tend to agree with those inferred from Love waves for GTSMs far from tidal water bodies, but to differ for GTSMs closer to coastlines. Orientations derived from teleseismic Love waves agree with those estimated by Grant and Langston (2010) using strains from a broadband seismic array near Anza, California. PBO GTSM recordings of teleseismic Love waves show differences of more than 20% among the shear-strain response coefficients of the four gauges. Love-wave derived orientations and relative shear-strain response coefficients can reduce uncertainties in shear strains derived from PBO GTSM data.

Depth to the Moho in Southern New England and Eastern New York State from Seismic Receiver Functions

NASA Astrophysics Data System (ADS)

Cipar, J. J.; Ebel, J.

2016-12-01

The thickness of the Earth's crust is a fundamental parameter of geophysics and geology. The eastern New York/southern New England area encompasses the suture between the Paleozoic Appalachian orogen and the Proterozoic Laurentian craton. The recent installation of the IRIS Traveling Array (TA) in 2013-2014 coupled with stations operated by Boston College, Lamont-Doherty, and the US National Seismic Network provide an unprecedented source of data for seismic studies of crustal structure. We use the receiver functions complied by the EarthScope Automated Receiver Survey (EARS) to measure crustal thickness. Our procedure is to stack receiver functions (RFs) at each station using the correct moveout for the P-to-S conversion at the Moho (Ps phase). The time difference between the Ps and direct P arrivals (Ps-P time) is dependent on crustal thickness (H) and crustal S-wave velocity (Vs). To get an estimate of H, we assume that the mean P-wave velocity (Vp) in the crust is 6.5 km/s, and determine the range of Vs for a range of Poisson's ratio (0.23-0.27). We then solve for H using the P-Ps times measured from the RF stacks (at Δ=60°) and our estimates for Vp and Vs. The uncertainty in S-wave velocity translates to approximately ±2 km uncertainty in crustal thickness. Our crustal thickness map shows the well-known general progression from shallow crust near the Atlantic coast line ( 30 km) to deeper crust (45+ km) in the Laurentian craton. However, some detailed features become evident on our map. Most notably, thin crust ( 30 km) extends inland from the coast to the Connecticut River valley in eastern-central Massachusetts and southeastern New Hampshire. The Berkshire Hills of western Massachusetts have thick crust (43 km), reaching as deep as 46 km in extreme northwestern Massachusetts. Thus, there is a 13-15 km increase in crustal thickness over a distance of about 60 km. Currently, no stations are located in that zone. We find that the eastern Adirondacks have very thick crust, generally in excess of 45 km. Overall, our crustal thickness measurements are in excellent agreement with those from the 1988 Ontario-New York-New England refraction experiment (USGS) and from a local receiver function study conducted using closely-spaced stations (John Schuh, Boston College).

New Insight into the Lithosphere Structure of the Gulf Coast of Texas and Louisiana

NASA Astrophysics Data System (ADS)

Pulliam, J.; Gurrola, H.; Mickus, K. L.; Keller, G. R.

2016-12-01

The Gulf Coast of Texas is a passive margin remaining after the breakup of Pangaea. The opening of the western Gulf of Mexico (GOM) was the result of the Yucatan block rifting away from North America and rotating to its present location but the exact nature of this rifting is not well understood. Some models describe it as passive rifting while other models consider it to be the result of active volcanic rifting. Until recently the sparse distribution of seismic stations limits our ability to image the deep crust and upper mantle that are important to the understanding of important tectonic process of the area. Here we present new observations from passive seismic imaging using data from a broadband 26-station profile across the Gulf Coastal Plain (GCP) and the EarthScope Transportable Array. Ps receiver function (RF) imaging of the GCP profile reveals possible remnants of a subducted slab beneath the GCP of the central Texas coast outboard of the Balcones fault zone. The presence of a remnant late Paleozoic slab associated with the assembly of Pangaea may imply that rifting associated with the opening of the GOM did not completely overprint older features, which suggests that passive rifting was responsible for the opening of western GOM. A remnant slab would provide a plausible explanation for a low velocity layer imaged beneath the coastal region by Sp RF imaging. A strong negative S110p phase observed in an Sp receiver functions image across the GCP of central Texas may be interpreted as the Lithosphere-Asthenosphere boundary (LAB) but observations of other positive and negative phases in the 110 and 200 km depth interval lead us to believe the interval is a semi-ductile region with layered flow. We refer to this interval as a "Lithosphere-Asthenosphere Transition Zone" (LATZ). The LATZ model is supported by observed high P but low S-wave velocities in this depth interval of tomographic models and by SKS analysis that inferred a large amount of anisotropy in the mantle beneath the GCP. Low velocity anomalies observed in Pn and body wave tomography models beneath the Southern Oklahoma Aulacogen (SOA) suggests flow of warm mantle material beneath the SOA from the Rockies and Rio Grande Rift toward the GCP; a direction consistent with the seismic anisotropy polarization inferred beneath the region from SKS splitting measurements.

Induced Earthquakes Are Not All Alike: Examples from Texas Since 2008 (Invited)

NASA Astrophysics Data System (ADS)

Frohlich, C.

2013-12-01

The EarthScope Transportable Array passed through Texas between 2008 and 2011, providing an opportunity to identify and accurately locate earthquakes near and/or within oil/gas fields and injection waste disposal operations. In five widely separated geographical locations, the results suggest seismic activity may be induced/triggered. However, the different regions exhibit different relationships between injection/production operations and seismic activity: In the Barnett Shale of northeast Texas, small earthquakes occurred only near higher-volume (volume rate > 150,000 BWPM) injection disposal wells. These included widely reported earthquakes occurring near Dallas-Fort Worth and Cleburne in 2008 and 2009. Near Alice in south Texas, M3.9 earthquakes occurred in 1997 and 2010 on the boundary of the Stratton Field, which had been highly productive for both oil and gas since the 1950's. Both earthquakes occurred during an era of net declining production, but their focal depths and location at the field boundary suggest an association with production activity. In the Eagle Ford of south central Texas, earthquakes occurred near wells following significant increases in extraction (water+produced oil) volumes as well as injection. The largest earthquake, the M4.8 Fashing earthquake of 20 October 2011, occurred after significant increases in extraction. In the Cogdell Field near Snyder (west Texas), a sequence of earthquakes beginning in 2006 followed significant increases in the injection of CO2 at nearby wells. The largest with M4.4 occurred on 11 September 2011. This is the largest known earthquake possibly attributable to CO2 injection. Near Timpson in east Texas a sequence of earthquakes beginning in 2008, including an M4.8 earthquake on 17 May 2012, occurred within three km of two high-volume injection disposal wells that had begun operation in 2007. These were the first known earthquakes at this location. In summary, the observations find possible induced/triggered earthquakes associated with recent increases in injection, recent increases in extraction, with CO2 injection, and with declining production. In all areas, during the 2008-2011 period there were no earthquakes occurring near vast majority of extraction/production wells; thus, the principal puzzle is why these activities sometimes induce seismicity and sometimes do not.

GSAC - Generic Seismic Application Computing

NASA Astrophysics Data System (ADS)

Herrmann, R. B.; Ammon, C. J.; Koper, K. D.

2004-12-01

With the success of the IRIS data management center, the use of large data sets in seismological research has become common. Such data sets, and especially the significantly larger data sets expected from EarthScope, present challenges for analysis with existing tools developed over the last 30 years. For much of the community, the primary format for data analysis is the Seismic Analysis Code (SAC) format developed by Lawrence Livermore National Laboratory. Although somewhat restrictive in meta-data storage, the simplicity and stability of the format has established it as an important component of seismological research. Tools for working with SAC files fall into two categories - custom research quality processing codes and shared display - processing tools such as SAC2000, MatSeis,etc., which were developed primarily for the needs of individual seismic research groups. While the current graphics display and platform dependence of SAC2000 may be resolved if the source code is released, the code complexity and the lack of large-data set analysis or even introductory tutorials could preclude code improvements and development of expertise in its use. We believe that there is a place for new, especially open source, tools. The GSAC effort is an approach that focuses on ease of use, computational speed, transportability, rapid addition of new features and openness so that new and advanced students, researchers and instructors can quickly browse and process large data sets. We highlight several approaches toward data processing under this model. gsac - part of the Computer Programs in Seismology 3.30 distribution has much of the functionality of SAC2000 and works on UNIX/LINUX/MacOS-X/Windows (CYGWIN). This is completely programmed in C from scratch, is small, fast, and easy to maintain and extend. It is command line based and is easily included within shell processing scripts. PySAC is a set of Python functions that allow easy access to SAC files and enable efficient manipulation of SAC files under a variety of operating systems. PySAC has proven to be valuable in organizing large data sets. An array processing package includes standard beamforming algorithms and a search based method for inference of slowness vectors. The search results can be visualized using GMT scripts output by the C programs, and the resulting snapshots can be combined into an animation of the time evolution of the 2D slowness field.

Observing the San Andreas Fault at Depth

NASA Astrophysics Data System (ADS)

Ellsworth, W.; Hickman, S.; Zoback, M.; Davis, E.; Gee, L.; Huggins, R.; Krug, R.; Lippus, C.; Malin, P.; Neuhauser, D.; Paulsson, B.; Shalev, E.; Vajapeyam, B.; Weiland, C.; Zumberge, M.

2005-12-01

Extending 4 km into the Earth along a diagonal path that crosses the divide between Salinian basement accreted to the Pacific Plate and Cretaceous sediments of North America, the main hole at the San Andreas Fault Observatory at Depth (SAFOD) was designed to provide a portal into the inner workings of a major plate boundary fault. The successful drilling and casing of the main hole in the summer of 2005 to a total vertical depth of 3.1 km make it possible to conduct spatially extensive and long-duration observations of active tectonic processes within the actively deforming core of the San Andreas Fault. In brief, the observatory consists of retrievable seismic, deformation and environmental sensors deployed inside the casing in both the main hole (maximum temperature 135 C) and the collocated pilot hole (1.1 km depth), and a fiber optic strainmeter installed behind casing in the main hole. By using retrievable systems deployed on either wire line or rigid tubing, each hole can be used for a wide range of scientific purposes, with instrumentation that takes maximum advantage of advances in sensor technology. To meet the scientific and technical challenges of building the observatory, borehole instrumentation systems developed for use in the petroleum industry and by the academic community in other deep research boreholes have been deployed in the SAFOD pilot hole and main hole over the past year. These systems included 15Hz omni-directional and 4.5 Hz gimbaled seismometers, micro-electro-mechanical accelerometers, tiltmeters, sigma-delta digitizers, and a fiber optic interferometeric strainmeter. A 1200-m-long, 3-component 80-level clamped seismic array was also operated in the main hole for 2 weeks of recording in May of 2005, collecting continuous seismic data at 4000 sps. Some of the observational highlights include capturing one of the M 2 SAFOD target repeating earthquakes in the near-field at a distance of 420 m, with accelerations of up to 200 cm/s and a static displacement of a few microns. Numerous other local events were observed over the summer by the tilt and seismic instruments in the pilot hole, some of which produced strain offsets of several nanostrain on the fiber optic strainmeter. We were fortunate to observe several episodes of non-volcanic tremor on the 80-level seismic array in May, 2005. These spatially unaliased recordings of the tremor wavefield reveal that the complex tremor time series is comprised of up-and down-going shear waves that produce a spatially stationary interference pattern over time scales of 10s of seconds. All data collected at SAFOD as part of the EarthScope project are open and freely available to all. The Northern California Earthquake Data Center at U.C. Berkeley is the principal data repository for SAFOD. The more than 2 TB of 80-level array data are also available at the IRIS DMC as an assembled data collection.

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Science.gov Websites

Array Funded Projects Geochronology Synthesis Workshops Scientific Publications Science Nuggets ES Synthesis Workshop 06-12 | 06-14 IRIS Workshop: Foundations, Frontiers, and Future Facilities for Seismology 06-15 | Call for Science Nuggets this spring! 07-26 | 07-28 Midcontinent Rift Synthesis Workshop See

Data Access and Web Services at the EarthScope Plate Boundary Observatory

NASA Astrophysics Data System (ADS)

Matykiewicz, J.; Anderson, G.; Henderson, D.; Hodgkinson, K.; Hoyt, B.; Lee, E.; Persson, E.; Torrez, D.; Smith, J.; Wright, J.; Jackson, M.

2007-12-01

The EarthScope Plate Boundary Observatory (PBO) at UNAVCO, Inc., part of the NSF-funded EarthScope project, is designed to study the three-dimensional strain field resulting from deformation across the active boundary zone between the Pacific and North American plates in the western United States. To meet these goals, PBO will install 880 continuous GPS stations, 103 borehole strainmeter stations, and five laser strainmeters, as well as manage data for 209 previously existing continuous GPS stations and one previously existing laser strainmeter. UNAVCO provides access to data products from these stations, as well as general information about the PBO project, via the PBO web site (http://pboweb.unavco.org). GPS and strainmeter data products can be found using a variety of access methods, incuding map searches, text searches, and station specific data retrieval. In addition, the PBO construction status is available via multiple mapping interfaces, including custom web based map widgets and Google Earth. Additional construction details can be accessed from PBO operational pages and station specific home pages. The current state of health for the PBO network is available with the statistical snap-shot, full map interfaces, tabular web based reports, and automatic data mining and alerts. UNAVCO is currently working to enhance the community access to this information by developing a web service framework for the discovery of data products, interfacing with operational engineers, and exposing data services to third party participants. In addition, UNAVCO, through the PBO project, provides advanced data management and monitoring systems for use by the community in operating geodetic networks in the United States and beyond. We will demonstrate these systems during the AGU meeting, and we welcome inquiries from the community at any time.

Dynamics and the Wilson Cycle: An EarthScope vision

NASA Astrophysics Data System (ADS)

Ebinger, Cynthia; Humphreys, Eugene; Williams, Michael; van der Lee, Suzan; Levin, Vadim; Webb, Laura; Becker, Thorsten

2017-04-01

Wilson's model has two major components, each with distinctive observables. Initial subduction of ocean lithosphere collides continents across a closing ocean basin, creating a mountain range; rifting then initiates within the collisional orogeny and progresses to create oceanic spreading and creation of a new ocean basin. Subduction eventually initiates near the old, cold, and heavily sedimented continental margin, leading to subduction, and repeating the cycle. This model is largely kinematic in nature, and predictive in application. We re-evaluate the Wilson Cycle in light of process-oriented perspectives afforded by the surface to mantle Earthscope results. Repeating episodes of mountain building by means of continental collisions remains clear, but new observations augment or diverge from Wilson's concepts. A 'new' component stems from observations from both the East and West coasts: translational fault systems played critical roles in continental accretion, collision, and rifting. Earthscope data sets also have enabled imaging of the structure of western U.S. lithosphere with unprecedented detail. From new and existing data sets, we conclude that collision occurs in 'ribbons' in large part linked to the shapes of the landmasses colliding landmasses, and deformation includes a major component of transform tectonics. Post-orogenic gravitational collapse may occur far inboard of the site of collision. A third 'new' feature is that plate coupling with the mantle leads to deformation outside the classic Wilson Cycle. For example, the passive margin of eastern N. America shows tectonic activity, uplift, and magmatism long after the onset of seafloor spreading, demonstrating the dynamic nature of lithosphere-asthenosphere coupling. A 'fourth' observation is that lateral density contrasts and volatile migration during subduction and collision effectively refertilize mantle lithosphere, and pre-condition later tectonic cycles.

UNAVCO: A Decade Supporting EarthScope - Three Decades of Supporting Geodesy for Science Innovation

NASA Astrophysics Data System (ADS)

Miller, M.

2013-12-01

UNAVCO supports research that establishes Earth's reference frame, enabling mapping of the planet's shape and mass; determines changes in the distribution of ice, water resources, and sea level; characterizes processes that contribute to natural and man-made hazards; and recognizes land-use changes (including subsidence, soil moisture, and health of wetlands). UNAVCO began as an investigator cooperative in 1984 - with the goal of sharing equipment and technologies that were expensive, rapidly changing, and extraordinarily powerful. Today as NSF's National Earth Science Geodetic Facility, on the eve of our 30th anniversary, we are excited to highlight a decade of support for major components of EarthScope, especially the Plate Boundary Observatory (PBO). Innovations by UNAVCO and the UNAVCO community have supported steady advancement towards millimeter-level global geodesy. Modern space geodesy provides new observational capability for contemporary deformation and magmatism in active convergent margin systems that operate over a spectrum of temporal and spatial scales, especially the PBO. Time scales vary from seconds to millennia, and spatial scales from borehole nanostrains to the global plate circuit. High-precision strain or 3-D point observations with borehole strainmeter or Global Positioning System (GPS) observations and geodetic imaging with SAR and LiDAR are used in combination to reveal these complex systems. GPS now combines with strong ground motion accelerometer time series to provide important enhancements to conventional seismology. The resulting 3-D fully georeferenced dynamic positioning time series are free of ambiguities associated with seismometer tilt and displacement. Geodesy constrains plate kinematics for convergence rate and direction, co-seismic deformation during great and moderate earthquakes, episodic tremor and slip events and related transient deformation, tectono-magmatic interactions, and the possible triggering effects of atmospheric or geomorphic unloading. Space geodesy furthers research on earthquake and tsunami hazards, volcanic eruptions, severe weather, hurricanes, coastal subsidence, wetlands health, soil moisture, groundwater distribution, and space weather. Of particular importance are contributions to the understanding of processes related to global warming and climate change, including sea level rise and dynamic changes in glaciers and large polar ice sheets. The discoveries of virtually every global geodesy study are supported - directly or indirectly - by some aspect of UNAVCO's work. Beyond research, a large international community of surveyors and civil engineers access UNAVCO data streams, software, and on-line resources daily. In a global society that is increasingly technology-dependent, consistently risk-averse, and often natural resource-limited, communities need geodetic research, education, and infrastructure to make informed decisions about living on a dynamic planet.

An emerging view of the crust and mantle of tectonic North America from EMScope: a mid- term progress review of Earthscope's magnetotelluric program

NASA Astrophysics Data System (ADS)

Schultz, A.; Bedrosian, P.; Evans, R.; Egbert, G.; Kelbert, A.; Mickus, K.; Livelybrooks, D.; Park, S.; Patro, P.; Peery, T.; Wannamaker, P.; Unsworth, M.; Weiss, C.; Woodward, B.

2008-12-01

EMScope, the MT component of the Earthscope project has completed its final year of infrastructure construction, and its third annual campaign of regional magnetotelluric array operations in the western USA. Seven semi-permanent "backbone" MT observatories have been installed in California, Oregon, Montana, New Mexico, Minnesota, Missouri and Virginia, designed through installation in 2 m deep, insulated underground vaults and with long, buried electric dipole detectors using stable electrodes, to provide extremely long-period magnetotelluric data meant to provide a set of regional, deep structural "anchor points" penetrating into the mid-mantle, in which a series of denser and more uniform regional, transportable MT networks can be tied. A total of 160 "transportable array" MT stations have been occupied in Oregon, Washington, Idaho, northernmost-California, and Montana. These were located on a 70 km quasi-regular grid, with coverage of Cascadia, parts of the Basin and Range, the Rockies and the Snake River Plain, the zone above a putative mantle plume that is hypothesized to serve as the magma source for both the Yellowstone supervolcano and a chain of volcanic features extending westward into Oregon. It is anticipated that in 2009 the transportable array will sweep eastward through the Yellowstone region, following which a set of regional transects at sites of special geodynamic interest will be staged. The transportable array stations are typically occupied for three weeks, providing MT response functions extending from 2-10,000 s or in cases as great as 20,000 s period. These stations are anchored at longer periods (extending as close to 100,000 s periods as possible) by the network of 7 backbone stations, to be operated continuously for up to five years. We present an initial set of 3-d inverse models from the EMScope data sets There is substantial coherence between the resulting 3-d conductivity model and the known boundaries of major physiographic provinces, as well as seismically delineated mid-to-lower crustal and upper mantle features. A combination of telemetry from backbone stations and frequent batch transmission of data from the transportable array field sites, followed by rapid data quality control procedures and generation of MT response functions provides a data set of use to all interested researchers. All EMScope data are made available freely through the IRIS Data Management Center or via the EMScope data portal. For transportable array sites these data are available typically within two weeks of acquisition.

Lithospheric radial anisotropy beneath the Gulf of Mexico

NASA Astrophysics Data System (ADS)

Chu, Risheng; Ko, Justin Yen-Ting; Wei, Shengji; Zhan, Zhongwen; Helmberger, Don

2017-05-01

The Lithosphere-Asthenosphere Boundary (LAB), where a layer of low viscosity asthenosphere decouples with the upper plate motion, plays an essential role in plate tectonics. Most dynamic modeling assumes that the shear velocity can be used as a surrogate for viscosity which provides key information about mantle flow. Here, we derive a shear velocity model for the LAB structure beneath the Gulf of Mexico allowing a detailed comparison with that beneath the Pacific (PAC) and Atlantic (ATL). Our study takes advantage of the USArray data from the March 25th, 2013 Guatemala earthquake at a depth of 200 km. Such data is unique in that we can observe a direct upward traveling lid arrival which remains the first arrival ahead of the triplications beyond 18°. This extra feature in conjunction with upper-mantle triplication sampling allows good depth control of the LAB and a new upper-mantle seismic model ATM, a modification of ATL, to be developed. ATM has a prominent low velocity zone similar to the structure beneath the western Atlantic. The model contains strong radial anisotropy in the lid where VSH is about 6% faster than VSV. This anisotropic feature ends at the bottom of the lithosphere at about the depth of 175 km in contrast to the Pacific where it extends to over 300 km. Another important feature of ATM is the weaker velocity gradient from the depth of 175 to 350 km compared to Pacific models, which may be related to differences in mantle flow.

S-to-P Conversions from Mid-mantle Slow Scatterers in Slab Regions: Observations of Deep/Stagnated Oceanic Crust?

NASA Astrophysics Data System (ADS)

He, Xiaobo; Zheng, Yixian

2018-02-01

The fate of a subducted slab is a key ingredient in the context of plate tectonics, yet it remains enigmatic especially in terms of its crustal component. In this study, our efforts are devoted to resolve slab-related structures in the mid-mantle below eastern Indonesia, the Izu-Bonin region, and the Peru area by employing seismic array analysing techniques on high-frequency waveform data from F-net in Japan and the Alaska regional network and the USArray in North America. A pronounced arrival after the direct P wave is observed in the recordings of four deep earthquakes (depths greater than 400 km) from three subduction systems including the Philippines, the Izu-Bonin, and the Peru. This later arrival displays a slightly lower slowness compared to the direct P wave and its back-azimuth deviates somewhat from the great-circle direction. We explain it as an S-to-P conversion at a deep scatterer below the sources in the source region. In total, five scatterers are seen at depths ranging from 930 to 1500 km. Those scatterers appear to be characterised by an 7 km-thick low-velocity layer compared to the ambient mantle. Combined evidence from published mineral physical analysis suggests that past subducted oceanic crust, possibly fragmented, is most likely responsible for these thin-layer compositional heterogeneities trapped in the mid-mantle beneath the study regions. Our observations give a clue to the potential fate of subducted oceanic crust.

Rayleigh Wave Phase Velocities in Alaska from Ambient Noise Tomography

NASA Astrophysics Data System (ADS)

Pepin, K. S.; Li, A.; Yao, Y.

2016-12-01

We have analyzed ambient noise data recorded at 136 broadband stations from the USArray Transportable Array and other permanent seismic networks in Alaska and westernmost Canada. Daily cross-correlations are obtained using vertical component seismograms and are stacked to form a single trace for each station pair. Rayleigh wave signals are extracted from the stacked traces and are used to calculate phase velocities in the Alaska region. Preliminary phase velocity maps show similar trends to those from previous studies, but also yield new anomalies given the wider geographical range provided by the Transportable Array. At short periods (6-12s), a high velocity anomaly is observed directly northeast of the Fairweather-Queen Charlotte fault, and a high velocity trend appears in the eastern Yukon terrane between the Denali and Tintina fault, probably reflecting mafic igneous crustal rocks. Significantly slow anomalies are present at the Prince William Sound, Cook Inlet, and the basins in southwestern and central Alaska, indicating sediment effects. The slow anomalies gradually shift to southeastern and south-central Alaska with increasing period (up to 40s), corresponding to the Wrangell volcano belt and the volcano arc near Cook Inlet. A broad high-velocity zone is also observed in central Alaska to the north of the Denali fault at long periods (30-40s). The Yakutat terrane is characterized as a high-velocity anomaly from period 14s to 25s but not imaged at longer periods due to poor resolution.

Gas injection may have triggered earthquakes in the Cogdell oil field, Texas

PubMed Central

Gan, Wei; Frohlich, Cliff

2013-01-01

Between 1957 and 1982, water flooding was conducted to improve petroleum production in the Cogdell oil field north of Snyder, TX, and a contemporary analysis concluded this induced earthquakes that occurred between 1975 and 1982. The National Earthquake Information Center detected no further activity between 1983 and 2005, but between 2006 and 2011 reported 18 earthquakes having magnitudes 3 and greater. To investigate these earthquakes, we analyzed data recorded by six temporary seismograph stations deployed by the USArray program, and identified 93 well-recorded earthquakes occurring between March 2009 and December 2010. Relocation with a double-difference method shows that most earthquakes occurred within several northeast–southwest-trending linear clusters, with trends corresponding to nodal planes of regional focal mechanisms, possibly indicating the presence of previously unidentified faults. We have evaluated data concerning injection and extraction of oil, water, and gas in the Cogdell field. Water injection cannot explain the 2006–2011 earthquakes, especially as net volumes (injection minus extraction) are significantly less than in the 1957–1982 period. However, since 2004 significant volumes of gases including supercritical CO2 have been injected into the Cogdell field. The timing of gas injection suggests it may have contributed to triggering the recent seismic activity. If so, this represents an instance where gas injection has triggered earthquakes having magnitudes 3 and larger. Further modeling studies may help evaluate recent assertions suggesting significant risks accompany large-scale carbon capture and storage as a strategy for managing climate change. PMID:24191019

Gas injection may have triggered earthquakes in the Cogdell oil field, Texas.

PubMed

Gan, Wei; Frohlich, Cliff

2013-11-19

Between 1957 and 1982, water flooding was conducted to improve petroleum production in the Cogdell oil field north of Snyder, TX, and a contemporary analysis concluded this induced earthquakes that occurred between 1975 and 1982. The National Earthquake Information Center detected no further activity between 1983 and 2005, but between 2006 and 2011 reported 18 earthquakes having magnitudes 3 and greater. To investigate these earthquakes, we analyzed data recorded by six temporary seismograph stations deployed by the USArray program, and identified 93 well-recorded earthquakes occurring between March 2009 and December 2010. Relocation with a double-difference method shows that most earthquakes occurred within several northeast-southwest-trending linear clusters, with trends corresponding to nodal planes of regional focal mechanisms, possibly indicating the presence of previously unidentified faults. We have evaluated data concerning injection and extraction of oil, water, and gas in the Cogdell field. Water injection cannot explain the 2006-2011 earthquakes, especially as net volumes (injection minus extraction) are significantly less than in the 1957-1982 period. However, since 2004 significant volumes of gases including supercritical CO2 have been injected into the Cogdell field. The timing of gas injection suggests it may have contributed to triggering the recent seismic activity. If so, this represents an instance where gas injection has triggered earthquakes having magnitudes 3 and larger. Further modeling studies may help evaluate recent assertions suggesting significant risks accompany large-scale carbon capture and storage as a strategy for managing climate change.

Preliminary results of receiver function analysis of seismic data recorded from a broadband deployment across the Gulf Coast Plain

NASA Astrophysics Data System (ADS)

Gurrola, H.; Pratt, K. W.; Pulliam, J.; Dunbar, J. A.

2011-12-01

In summer of 2010, 21 broadband seismographs were installed at 16-18 km spacing along a transect running from Johnson City, TX, (on the Edwards Plateau), to Matagorda Island to study the current structure of this rifted passive margin. The large magnetic anomaly that parallels the coast throughout the Gulf region moves on-shore beneath our transect such that we will be able to investigate the source of this anomaly. A second important target that will be imaged in this Balcones fault which is associated with the Ouachita front. This project is funded by a grant from the Norman Hackerman Advanced Research Program (NHARP), a biannual competition among Texas Universities to support research, and makes use of Texas Tech, Baylor, and UT Austin equipment. As a result, the deployment includes a less uniform array of seismic equipment, (10 Trillium compact seismometers and 10 Guralps; including 40Ts, 3Ts and 3ESPs), than projects supported by the IRIS PASSCAL center. Our vault construction was similar to Flexible array vaults, but Gulf Coast provides a more challenging environment for deployment than most encountered in the western US. The shallow water table and loose sediment can become almost fluid when storms deluge the area with rain. In dry periods, mud cracks near the vaults cause the vaults to tilt. As a result, even high quality, shallow seismic vaults can "float" or shift sufficiently to cause one or two components of the seismic stations to drift against their stops in days or weeks. As a result, the only data consistently available from all our stations, are vertical components. Horizontal component data from the summer of 2010 can be hit and miss due to the tilting of the vaults. These issues have been reduced in the summer of 2011 due to the drought. To address the data's shortcomings, we will average the vertical components from our stations and nearby EarthScope TA stations, (up 300 km away), to isolate the cleanest representation of the incoming P-wave, (with local PPp reverberations averaged out). This is essentially beam forming for the optimal teleseismic ray path. The clean P-wave will then be deconvolved from the vertical components at each station to produce a vertical component receiver function that will enable us to model and stack local P-wave reverberations to produce a 2-D image of lithospheric structure. To produce traditional receiver functions from time periods where one component is lost from several stations, we will treat neighboring stations as arrays and recover an "array averaged three-component seismogram" for each loacation. These "beamed" seismograms will allow imaging of the crust, lithospheric mantle, and transition zone beneath the broadband array using traditional receiver function stacking or migration.

EarthScope's Education, Outreach, and Communications: Using Social Media from Continental to Global Scales

NASA Astrophysics Data System (ADS)

Bohon, W.; Frus, R.; Arrowsmith, R.; Fouch, M. J.; Garnero, E. J.; Semken, S. C.; Taylor, W. L.

2011-12-01

Social media has emerged as a popular and effective form of communication among all age groups, with nearly half of Internet users belonging to a social network or using another form of social media on a regular basis. This phenomenon creates an excellent opportunity for earth science organizations to use the wide reach, functionality and informal environment of social media platforms to disseminate important scientific information, create brand recognition, and establish trust with users. Further, social media systems can be utilized for missions of education, outreach, and communicating important timely information (e.g., news agencies are common users). They are eminently scaleable (thus serving from a few to millions of users with no cost and no performance problem), searchable (people are turning to them more frequently as conduits for information), and user friendly (thanks to the massive resources poured into the underlying technology and design, these systems are easy to use and have been widely adopted). They can be used, therefore, to engage the public interactively with the EarthScope facilities, experiments, and discoveries, and continue the cycle of discussions, experiments, analysis and conclusions that typify scientific advancement. The EarthScope National Office (ESNO) is launching an effort to utilize social media to broaden its impact as a conduit between scientists, facilities, educators, and the public. The ESNO will use the opportunities that social media affords to offer high quality science content in a variety of formats that appeal to social media users of various age groups, including blogs (popular with users 18-29), Facebook and Twitter updates (popular with users ages 18-50), email updates (popular with older adults), and video clips (popular with all age groups). We will monitor the number of "fans" and "friends" on social media and networking pages in order to gauge the increase in the percentage of the user population visiting the site. We will also use existing tools available on social media sites to track the relationships between users who visit or "friend" the site to determine how knowledge of the site is transferred amongst various social, educational or geographic groups. Finally, we will use this information to iteratively improve the variety of content and media on the site to increase our user pool, improve EarthScope recognition, and provide appropriate and user-specific Earth science information, especially for time sensitive events of wide interest such as natural disasters.

Earthquake source imaging by high-resolution array analysis at regional distances: the 2010 M7 Haiti earthquake as seen by the Venezuela National Seismic Network

NASA Astrophysics Data System (ADS)

Meng, L.; Ampuero, J. P.; Rendon, H.

2010-12-01

Back projection of teleseismic waves based on array processing has become a popular technique for earthquake source imaging,in particular to track the areas of the source that generate the strongest high frequency radiation. The technique has been previously applied to study the rupture process of the Sumatra earthquake and the supershear rupture of the Kunlun earthquakes. Here we attempt to image the Haiti earthquake using the data recorded by Venezuela National Seismic Network (VNSN). The network is composed of 22 broad-band stations with an East-West oriented geometry, and is located approximately 10 degrees away from Haiti in the perpendicular direction to the Enriquillo fault strike. This is the first opportunity to exploit the privileged position of the VNSN to study large earthquake ruptures in the Caribbean region. This is also a great opportunity to explore the back projection scheme of the crustal Pn phase at regional distances,which provides unique complementary insights to the teleseismic source inversions. The challenge in the analysis of the 2010 M7.0 Haiti earthquake is its very compact source region, possibly shorter than 30km, which is below the resolution limit of standard back projection techniques based on beamforming. Results of back projection analysis using the teleseismic USarray data reveal little details of the rupture process. To overcome the classical resolution limit we explored the Multiple Signal Classification method (MUSIC), a high-resolution array processing technique based on the signal-noise orthognality in the eigen space of the data covariance, which achieves both enhanced resolution and better ability to resolve closely spaced sources. We experiment with various synthetic earthquake scenarios to test the resolution. We find that MUSIC provides at least 3 times higher resolution than beamforming. We also study the inherent bias due to the interferences of coherent Green’s functions, which leads to a potential quantification of biased uncertainty of the back projection. Preliminary results from the Venezuela data set shows an East to West rupture propagation along the fault with sub-Rayleigh rupture speed, consistent with a compact source with two significant asperities which are confirmed by source time function obtained from Green’s function deconvolution and other source inversion results. These efforts could lead the Venezuela National Seismic Network to play a prominent role in the timely characterization of the rupture process of large earthquakes in the Caribbean, including the future ruptures along the yet unbroken segments of the Enriquillo fault system.

Statistical discrimination of induced and tectonic earthquake sequences in Central and Eastern US based on waveform detected catalogs

NASA Astrophysics Data System (ADS)

Meng, X.; Daniels, C.; Smith, E.; Peng, Z.; Chen, X.; Wagner, L. S.; Fischer, K. M.; Hawman, R. B.

2015-12-01

Since 2001, the number of M>3 earthquakes increased significantly in Central and Eastern United States (CEUS), likely due to waste-water injection, also known as "induced earthquakes" [Ellsworth, 2013]. Because induced earthquakes are driven by short-term external forcing and hence may behave like earthquake swarms, which are not well characterized by branching point-process models, such as the Epidemic Type Aftershock Sequence (ETAS) model [Ogata, 1988]. In this study we focus on the 02/15/2014 M4.1 South Carolina and the 06/16/2014 M4.3 Oklahoma earthquakes, which likely represent intraplate tectonic and induced events, respectively. For the South Carolina event, only one M3.0 aftershock is identified by the ANSS catalog, which may be caused by a lack of low-magnitude events in this catalog. We apply a recently developed matched filter technique to detect earthquakes from 02/08/2014 to 02/22/2014 around the epicentral region. 15 seismic stations (both permanent and temporary USArray networks) within 100 km of the mainshock are used for detection. The mainshock and aftershock are used as templates for the initial detection. Newly detected events are employed as new templates, and the same detection procedure repeats until no new event can be added. Overall we have identified more than 10 events, including one foreshock occurred ~11 min before the M4.1 mainshock. However, the numbers of aftershocks are still much less than predicted with the modified Bath's law. For the Oklahoma event, we use 1270 events from the ANSS catalog and 182 events from a relocated catalog as templates to scan through continuous recordings 3 days before to 7 days after the mainshock. 12 seismic stations within the vicinity of the mainshock are included in the study. After obtaining more complete catalogs for both sequences, we plan to compare the statistical parameters (e.g., b, a, K, and p values) between the two sequences, as well as their spatial-temporal migration pattern, which may shed light on the underlying physics of tectonic and induced earthquakes.

Mapping the upper mantle beneath North American continent with joint inversion of surface-wave phase and amplitude

NASA Astrophysics Data System (ADS)

Yoshizawa, K.; Hamada, K.

2017-12-01

A new 3-D S-wave model of the North American upper mantle is constructed from a large number of inter-station phase and amplitude measurements of surface waves. A fully nonlinear waveform fitting method by Hamada and Yoshizawa (2015, GJI) is applied to USArray for measuring inter-station phase speeds and amplitude ratios of the fundamental-mode Rayleigh and Love waves. We employed the seismic events from 2007 - 2014 with Mw 6.0 or greater, and collected a large-number of inter-station phase speed data (about 130,000 for Rayleigh and 85,000 for Love waves) and amplitude ratio data (about 75,000 for Rayleigh waves) in a period range from 30 to 130 s for fundamental-mode surface waves. Typical inter-station distances are mostly in a range between 300 and 800 km, which can be of help in enhancing the lateral resolution of a regional tomography model. We first invert Rayleigh-wave phase speeds and amplitudes simultaneously for phase speed maps as well as local amplification factors at receiver locations. The isotropic 3-D S-wave model constructed from these phase speed maps incorporating both phase and amplitude data exhibits better recovery of the strength of velocity perturbations. In particular, local tectonic features characterized by strong velocity gradients, such as Rio Grande Rift, Colorado Plateau and New Madrid Seismic Zone, are more enhanced than conventional models derived from phase information only. The results indicate that surface-wave amplitude, which is sensitive to the second derivative of phase speeds, can be of great help in retrieving small-scale heterogeneity in the upper mantle. We also obtain a radial anisotropy model from the simultaneous inversions of Rayleigh and Love waves (without amplitude information). The model has shown faster SH wave speed anomalies than SV above the depth of 100 km, particularly in tectonically active regions in the western and central U.S., representing the effects of current and former tectonic processes on anisotropic properties in the continental lithosphere.

Shear Wave Structure in the Lithosphere of Texas from Ambient Noise Tomography

NASA Astrophysics Data System (ADS)

Yao, Y.; Li, A.

2014-12-01

Texas contains several distinct tectonic provinces, the Laurentia craton, the Ouachita belt, and the Gulf coastal plain. Although numerous geophysical experiments have been conducted in Texas for petroleum exploration, the lithosphere structure of Texas has not been well studied. We present here the Texas-wide shear wave structure using seismic ambient noise data recorded at 87 stations from the Transportable Array of the USArray between March 2010 and February 2011. Rayleigh wave phase velocities between pairs of stations are obtained by cross-correlating long ambient noise sequences and are used to develop phase velocity maps from 6 to 40 s. These measured phase velocities are used to construct 1-D and 3-D shear wave velocity models, which consist of four crust layers and one upper mantle layer. Shear wave velocity maps reveal a close correlation with major geological features. From the surface to 25 km depth, Positive anomalies coincide with the Laurentia craton, and negative anomalies coincide with the continental margin. The boundary of positive-negative anomaly perfectly matches the Ouachita belt. The Llano Uplift is imaged as the highest velocity through the mid-crust because the igneous rock forming the uplift has faster seismic velocity than the normal continental crust. Similarly, three small high-velocity areas exist beneath the Waco Uplift, Devils River Uplift, and Benton Uplift, even though surface geological traces are absent in these areas. The lowest velocity at the shallow crust appears in northeastern and southeastern Texas separated by the San Marcos Arch, correlating with thick sediment layers. An exceptional low velocity is imaged in southernmost Texas in the lower crust and upper mantle, probably caused by subducted wet oceanic crust before the rifting in the Gulf of Mexico. In the uppermost mantle, positive shear wave anomalies extend southeastward from the Ouachita belt to the Gulf coast, likely evidencing the subducted oceanic lithosphere during the Ouachita orogeny. This observation need be further tested using long period surface wave dispersions from earthquakes, which help to improve model resolution in the upper mantle.

Lithospheric discontinuities beneath the U.S. Midcontinent - signatures of Proterozoic terrane accretion and failed rifting

NASA Astrophysics Data System (ADS)

Chen, Chen; Gilbert, Hersh; Fischer, Karen M.; Andronicos, Christopher L.; Pavlis, Gary L.; Hamburger, Michael W.; Marshak, Stephen; Larson, Timothy; Yang, Xiaotao

2018-01-01

Seismic discontinuities between the Moho and the inferred lithosphere-asthenosphere boundary (LAB) are known as mid-lithospheric discontinuities (MLDs) and have been ascribed to a variety of phenomena that are critical to understanding lithospheric growth and evolution. In this study, we used S-to-P converted waves recorded by the USArray Transportable Array and the OIINK (Ozarks-Illinois-Indiana-Kentucky) Flexible Array to investigate lithospheric structure beneath the central U.S. This region, a portion of North America's cratonic platform, provides an opportunity to explore how terrane accretion, cratonization, and subsequent rifting may have influenced lithospheric structure. The 3D common conversion point (CCP) volume produced by stacking back-projected Sp receiver functions reveals a general absence of negative converted phases at the depths of the LAB across much of the central U.S. This observation suggests a gradual velocity decrease between the lithosphere and asthenosphere. Within the lithosphere, the CCP stacks display negative arrivals at depths between 65 km and 125 km. We interpret these as MLDs resulting from the top of a layer of crystallized melts (sill-like igneous intrusions) or otherwise chemically modified lithosphere that is enriched in water and/or hydrous minerals. Chemical modification in this manner would cause a weak layer in the lithosphere that marks the MLDs. The depth and amplitude of negative MLD phases vary significantly both within and between the physiographic provinces of the midcontinent. Double, or overlapping, MLDs can be seen along Precambrian terrane boundaries and appear to result from stacked or imbricated lithospheric blocks. A prominent negative Sp phase can be clearly identified at 80 km depth within the Reelfoot Rift. This arrival aligns with the top of a zone of low shear-wave velocities, which suggests that it marks an unusually shallow seismic LAB for the midcontinent. This boundary would correspond to the top of a region of mechanically and chemically rejuvenated mantle that was likely emplaced during late Precambrian/early Cambrian rifting. These observations suggest that the lithospheric structure beneath the Reelfoot Rift may be an example of a global phenomenon in which MLDs act as weak zones that facilitate the removal of cratonic lithosphere that lies beneath.

Advances in Global Adjoint Tomography - Data Assimilation and Inversion Strategy

NASA Astrophysics Data System (ADS)

Ruan, Y.; Lei, W.; Lefebvre, M. P.; Modrak, R. T.; Smith, J. A.; Bozdag, E.; Tromp, J.

2016-12-01

Seismic tomography provides the most direct way to understand Earth's interior by imaging elastic heterogeneity, anisotropy and anelasticity. Resolving thefine structure of these properties requires accurate simulations of seismic wave propagation in complex 3-D Earth models. On the supercomputer "Titan" at Oak Ridge National Laboratory, we are employing a spectral-element method (Komatitsch & Tromp 1999, 2002) in combination with an adjoint method (Tromp et al., 2005) to accurately calculate theoretical seismograms and Frechet derivatives. Using 253 carefully selected events, Bozdag et al. (2016) iteratively determined a transversely isotropic earth model (GLAD_M15) using 15 preconditioned conjugate-gradient iterations. To obtain higher resolution images of the mantle, we have expanded our database to more than 4,220 Mw5.0-7.0 events occurred between 1995 and 2014. Instead of using the entire database all at once, we choose to draw subsets of about 1,000 events from our database for each iteration to achieve a faster convergence rate with limited computing resources. To provide good coverage of deep structures, we selected approximately 700 deep and intermedia earthquakes and 300 shallow events to start a new iteration. We reinverted the CMT solutions of these events in the latest model, and recalculated synthetic seismograms. Using the synthetics as reference seismograms, we selected time windows that show good agreement with data and make measurements within the windows. From the measurements we further assess the overall quality of each event and station, and exclude bad measurements base upon certain criteria. So far, with very conservative criteria, we have assimilated more than 8.0 million windows from 1,000 earthquakes in three period bands for the new iteration. For subsequent iterations, we will change the period bands and window selecting criteria to include more window. In the inversion, dense array data (e.g., USArray) usually dominate model updates. In order to better handle this issue, we introduced weighting of stations and events based upon their relative distance and showed that the contribution from dense array is better balanced in the Frechet derivatives. We will present a summary of this form of data assimilation and preliminary results of the first few iterations.

Multi-scale mantle structure underneath the Americas from a new tomographic model of seismic shear velocity

NASA Astrophysics Data System (ADS)

Porritt, R. W.; Becker, T. W.; Auer, L.; Boschi, L.

2017-12-01

We present a whole-mantle, variable resolution, shear-wave tomography model based on newly available and existing seismological datasets including regional body-wave delay times and multi-mode Rayleigh and Love wave phase delays. Our body wave dataset includes 160,000 S wave delays used in the DNA13 regional tomographic model focused on the western and central US, 86,000 S and SKS delays measured on stations in western South America (Porritt et al., in prep), and 3,900,000 S+ phases measured by correlation between data observed at stations in the IRIS global networks (IU, II) and stations in the continuous US, against synthetic data generated with IRIS Syngine. The surface wave dataset includes fundamental mode and overtone Rayleigh wave data from Schaeffer and Levedev (2014), ambient noise derived Rayleigh wave and Love wave measurements from Ekstrom (2013), newly computed fundamental mode ambient noise Rayleigh wave phase delays for the continuous US up to July 2017, and other, previously published, measurements. These datasets, along with a data-adaptive parameterization utilized for the SAVANI model (Auer et al., 2014), should allow significantly finer-scale imaging than previous global models, rivaling that of regional-scale approaches, under the USArray footprint in the continuous US, while seamlessly integrating into a global model. We parameterize the model for both vertically (vSV) and horizontally (vSH) polarized shear velocities by accounting for the different sensitivities of the various phases and wave types. The resulting, radially anisotropic model should allow for a range of new geodynamic analysis, including estimates of mantle flow induced topography or seismic anisotropy, without generating artifacts due to edge effects, or requiring assumptions about the structure of the region outside the well resolved model space. Our model shows a number of features, including indications of the effects of edge-driven convection in the Cordillera and along the eastern margin and larger-scale convection due to the subduction of the Farallon slab and along the edge of the Laurentia cratonic margin.

Seismic Structure in the Vicinity of the Inner Core Boundary beneath northeastern Asia

NASA Astrophysics Data System (ADS)

Ibourichene, A. S.; Romanowicz, B. A.

2016-12-01

The inner core boundary (ICB) separates the solid inner core from the liquid outer core. The crystallization of iron occurring at this limit induces the expulsion of lighter elements such as H, O, S, Si into the outer core, generating chemically-driven convection, which provides power for the geodynamo. Both the F layer, right above the ICB, and the uppermost inner core, are affected by this process so that their properties provide important constraints for a better understanding of core dynamics and, ultimately, the generation and sustained character of the earth's magnetic field. In this study, we investigate the evolution of model parameters (P-velocity, density and quality factor) with depth in the vicinity of the ICB. For this purpose, we combine observations of two body wave phases sensitive to this region: the PKP(DF) phase refracted in the inner core and the PKiKP reflected on the ICB. Variations in the PKP(DF)/PKiKP amplitude ratio and PKP(DF)-PKiKP differential travel times can be related to structure around the ICB. We use waveform data from earthquakes located in Sumatra and recorded by the dense USArray seismic network, which allows us to sample ICB structure beneath northeastern Asia. Observed waveforms are compared to synthetics computed using the DSM method (e.g., Geller et Takeuchi, 1995) in model AK135 (e.g., Montagner & Kennett, 1996) in order to measure amplitude and travel time anomalies. Previous studies (e.g., Tanaka, 1997 ; Cao and Romanowicz, 2004, Yu and Wen, 2006; Waszek and Deuss, 2011) have observed an hemispherical pattern in the vicinity of the ICB exhibiting a faster and more attenuated eastern hemisphere compared to the western hemisphere. The region studied is located in the eastern hemisphere. We find that, on average, travel time anomalies are consistent with previous studies of the eastern hemisphere, however, amplitude ratios are not. We conduct a parameter search for the 1D model that best fits our data. We also consider fluctuations around this best fitting average model and quantify the statistical properties of the short wavelength fluctuations.

Studies of earthquakes stress drops, seismic scattering, and dynamic triggering in North America

NASA Astrophysics Data System (ADS)

Escudero Ayala, Christian Rene

I use the Relative Source Time Function (RSTF) method to determine the source properties of earthquakes within southeastern Alaska-northwestern Canada in a first part of the project, and earthquakes within the Denali fault in a second part. I deconvolve a small event P-arrival signal from a larger event by the following method: select arrivals with a tapered cosine window, fast fourier transform to obtain the spectrum, apply water level deconvolution technique, and bandpass filter before inverse transforming the result to obtain the RSTF. I compare the source processes of earthquakes within the area to determine stress drop differences to determine their relation with the tectonic setting of the earthquakes location. Results show an consistency with previous results, stress drop independent of moment implying self-similarity, correlation of stress drop with tectonic regime, stress drop independent of depth, stress drop depends of focal mechanism where strike-slip present larger stress drops, and decreasing stress drop as function of time. I determine seismic wave attenuation in the central western United States using coda waves. I select approximately 40 moderate earthquakes (magnitude between 5.5 and 6.5) located alocated along the California-Baja California, California-Nevada, Eastern Idaho, Gulf of California, Hebgen Lake, Montana, Nevada, New Mexico, off coast of Northern California, off coast of Oregon, southern California, southern Illinois, Vancouver Island, Washington, and Wyoming regions. These events were recorded by the EarthScope transportable array (TA) network from 2005 to 2009. We obtain the data from the Incorporated Research Institutions for Seismology (IRIS). In this study we implement a method based on the assumption that coda waves are single backscattered waves from randomly distributed heterogeneities to calculate the coda Q. The frequencies studied lie between 1 and 15 Hz. The scattering attenuation is calculated for frequency bands centered at 1.5, 3, 5, 7.5, 10.5, and 13.5 Hz. Coda Q present a great correlation with tectonic and geology setting, as well as the crustal thickness. I analyze global and Middle American Subduction Zone (MASZ) seismicity from 1998 to 2008 to quantify the transient stresses effects at teleseismic distances. I use the Bulletin of the International Seismological Centre Catalog (ISCCD) published by the Incorporated Research Institutions for Seismology (IRIS). To identify MASZ seismicity changes due to distant, large (Mw ¿ 7) earthquakes, I first identify local earthquakes that occurred before and after the mainshocks. I then group the local earthquakes within a cluster radius between 75 to 200 km. I obtain statistics based on characteristics of both mainshocks and local earthquakes clusters, such as cluster-mainshock azimuth, mainshock focal mechanism, and local earthquakes clusters within the MASZ. Based on the lateral variations of the dip along the subducted oceanic plate, I divide the Mexican subduction zone into four segments. I then apply the Paired Samples Statistical Test (PSST) to the sorted data to identify increment, decrement or either in the local seismicity associated with distant large earthquakes passage of surface waves. I identify dynamic triggering for all MASZ segments produced by large earthquakes emerging from specific azimuths, as well as, a decrease for some cases. I find no dependence of seismicity changes on mainshock focal mechanism.

Subgrid geoelectric field specification for GIC modeling

NASA Astrophysics Data System (ADS)

Butala, M.; Grawe, M.; Kamalabadi, F.; Makela, J. J.

2017-12-01

Geomagnetically induced currents (GICs) result from surface geomagnetic field (ěc{B}) variation driven by space weather disturbances. For the most intense disturbances, the consequences can range from power grid instability to even widespread failure. Modeling GICs to assess vulnerability requires the specification of the surface geoelectric field (ěc{E}) at all spatial locations coincident with the electric power system. In this study, we investigate how to best reproduce ěc{E} given the available sparse, irregularly spaced magnetometer measurements of ěc{B} and suitable electromagnetic transfer functions (EMTFs) to transform the local ěc{B} to ěc{E}. The assessment is made against ground truth from publicly available ěc{E} measurements provided by the EarthScope magnetotelluric (MT) array, a set of 7 fixed and several transportable joint ěc{B} and ěc{E} sensors. The scope of this study spans several dimensions: geomagnetic disturbance intensity, spatial interpolation scheme, and EMTF type, i.e., 1-D models based on studies of local geology and 3-D models derived from the EarthScope MT data.

Three-Dimensional Magnetotelluric Imaging of the Cascadia Subduction Zone with an Amphibious Array

NASA Astrophysics Data System (ADS)

Egbert, G. D.; Yang, B.; Bedrosian, P.; Kelbert, A.; Key, K.; Livelybrooks, D.; Parris, B. A.; Schultz, A.

2017-12-01

We present results from three-dimensional inversion of an amphibious magnetotelluric (MT) array consisting of 71 offshore and 75 onshore sites in the central part of Cascadia, to image down-dip and along strike variations of electrical conductivity, and to constrain the 3D distribution of fluids and melt in the subduction zone. The array is augmented by EarthScope TA MT data and legacy 2D profiles providing sparser coverage of western WA, OR, and northern CA. The prior model for the inversion includes ocean bathymetry, conductive marine sediments, and a resistive subducting plate, with geometry derived from the model of McCrory et al. (2012) and seismic tomography. Highly conductive features appear just above the interface with the a priori resistive plate in three zones. (1) In the area with marine MT data a conductive layer, which we associate with fluid-rich decollement and subduction channel sediments, extends eastward from the trench to underthrust the seaward edge of Siletzia, which is clearly seen as a thick crustal resistor. The downdip extent of the underthrust conductive layer is a remarkably uniform 35 km. (2) High conductivities, consistent with metamorphic fluids associated with eclogitization, occur near the forearc mantle corner. Conductivity is highly variable along strike, organized in a series of E-W to diagonal elongated conductive/resistive structures, whose significance remains enigmatic. (3) High conductivities associated with fluids and melts are found in the backarc, again exhibiting substantial along strike variability.

Outreach on a National Scale: The Critical Role of Facilities

NASA Astrophysics Data System (ADS)

Bartel, B. A.; Charlevoix, D. J.

2015-12-01

Facilities provide infrastructure for science that would not be feasible at a single institution. Facilities are also a resource for development of outreach products and activities that reach a national audience of diverse stakeholders. UNAVCO manages the NSF geodetic facility GAGE (Geodesy Advancing Geosciences and Earthscope). Staff at UNAVCO with expertise in education, outreach, and communication translate the science and supporting infrastructure into materials consumable by a wide array of users including teachers, students, museum attendees, emergency managers, park interpreters, and members of the general public. UNAVCO has the ability to distribute materials to a national and international audience, thereby greatly increasing the impact of the science and increasing the value of the investment by the National Science Foundation. In 2014 and 2015, UNAVCO produced multiple print products focused on the Plate Boundary Observatory (PBO), the geodetic component of EarthScope. Products include a deck of playing cards featuring PBO GPS stations, a poster featuring GPS velocities of the Western United States, and another poster focused on GPS velocities in Alaska. We are distributing these products to a broad audience, including teachers, station permit holders, and community members. The Tectonics of the Western United States poster was distributed this year in the American Geosciences Institute Earth Science Week kit for teachers, reaching 16,000 educators around the country. These posters and the PBO playing cards (PBO-52) were distributed to more than 100 teachers through workshops led by UNAVCO, the EarthScope National Office, the Southern California Earthquake Center (SCEC), and more. Additionally, these cards serve as a way to engage landowners who host these scientific stations on their property. This presentation will address the strategies for creating nationally relevant materials and the tools used for dissemination of materials to a broad audience. We will outline the process of our planning strategy as well as share ways in which we evaluate impact of particular outreach products and the overall outreach program.

Rayleigh-wave phase-velocity maps and three-dimensional shear velocity structure of the western US from local non-plane surface wave tomography

USGS Publications Warehouse

Pollitz, F.F.; Snoke, J. Arthur

2010-01-01

We utilize two-and-three-quarter years of vertical-component recordings made by the Transportable Array (TA) component of Earthscope to constrain three-dimensional (3-D) seismic shear wave velocity structure in the upper 200 km of the western United States. Single-taper spectral estimation is used to compile measurements of complex spectral amplitudes from 44 317 seismograms generated by 123 teleseismic events. In the first step employed to determine the Rayleigh-wave phase-velocity structure, we implement a new tomographic method, which is simpler and more robust than scattering-based methods (e.g. multi-plane surface wave tomography). The TA is effectively implemented as a large number of local arrays by defining a horizontal Gaussian smoothing distance that weights observations near a given target point. The complex spectral-amplitude measurements are interpreted with the spherical Helmholtz equation using local observations about a succession of target points, resulting in Rayleigh-wave phase-velocity maps at periods over the range of 18–125 s. The derived maps depend on the form of local fits to the Helmholtz equation, which generally involve the nonplane-wave solutions of Friederich et al. In a second step, the phase-velocity maps are used to derive 3-D shear velocity structure. The 3-D velocity images confirm details witnessed in prior body-wave and surface-wave studies and reveal new structures, including a deep (>100 km deep) high-velocity lineament, of width ∼200 km, stretching from the southern Great Valley to northern Utah that may be a relic of plate subduction or, alternatively, either a remnant of the Mojave Precambrian Province or a mantle downwelling. Mantle seismic velocity is highly correlated with heat flow, Holocene volcanism, elastic plate thickness and seismicity. This suggests that shallow mantle structure provides the heat source for associated magmatism, as well as thinning of the thermal lithosphere, leading to relatively high stress concentration. Our images also confirm the presence of high-velocity mantle at 100 km depth beneath areas of suspected mantle delamination (southern Sierra Nevada; Grande Ronde uplift), low velocity mantle underlying active rift zones, and high velocity mantle associated with the subducting Juan de Fuca plate. Structure established during the Proterozoic appears to exert a lasting influence on subsequent volcanism and tectonism up to the Present.

Infrasonic Signals from the 29 June 2012 Derecho

NASA Astrophysics Data System (ADS)

Winslow, N.; Howard, W. B.; Pulli, J. J.; Kofford, A. S.

2012-12-01

Common weather events such as pressure fronts, tornados, and hurricanes generate infrasonic signals (sub-audible acoustic signals with an oscillatory frequency below 20 Hz). These signals can provide a distal (>10km) analysis of weather events because: (1) the attenuation of an infrasonic signal with distance is less than that of a similar audible signal, and (2) the propagation velocities of typical weather events are much slower than the speed of sound. The 29 June, 2012 Derecho (a widespread, long-lived, rapidly moving linear band of storms extending more than 240 miles and including wind gusts in excess of 58 mph) that stretched from Chicago, IL to Washington, DC generated infrasonic signals in addition to causing over $100 million in damage to the power systems of Virginia, West Virginia, and Maryland alone. The infrasonic (and seismic) signals from this event were recorded on the NCPA micro barometers along the northeastern edge of the current configuration of the USArray. These instruments, which sample at 40 Hz, exhibit a flat frequency response from around 0.1 Hz to above 20 Hz and show a sensitivity of 1.57 x 104 Volts/Pascal at 0.8 Hz. An analysis of the recordings observed at multiple stations identified several infrasonic signatures from the Derecho. The signal's duration was approximately 40 minutes and exhibited a large peak pressure fluctuation. A characteristic ramp up occurred before the peak pressure fluctuation, and the majority of the infrasonic energy occurred below 1 Hz. These signatures are analyzed within the context of the Derecho as an infrasonic source, and the propagation of infrasound in the atmosphere.

Crustal thickness and Vp/Vs beneath the southeastern United States: Constraints from receiver function stacking

NASA Astrophysics Data System (ADS)

Yang, Q.; Gao, S. S.; Liu, K. H.

2017-12-01

To provide new constraints on crustal structure and evolution models beneath a collage of tectonic provinces in the southeastern United States, a total of 10,753 teleseismic receiver functions recorded by 125 USArray and other seismic stations are used to compute crustal thickness and Vp/Vs values. The resulting crustal thicknesses range from 25 km at the coast to 51 km beneath the peak of the southern Appalachians with an average of 36.2 km ± 5.5 km. The resulting crustal thicknesses correlate well with surface elevation and Bouguer gravity anomalies. Beneath the Atlantic Coastal Plain, the crustal thicknesses show a clear eastward thinning with a magnitude of 10 km, from about 40 km beneath the western margin to 30 km beneath the coast. The Vp/Vs values for the entire study area range from 1.71 to 1.90 with a mean value of 1.80 ± 0.04. The mean Vp/Vs value is 1.82±0.035 in the southern Appalachian Mountain. The slightly larger than normal crustal Vp/Vs for this area might be the result of significant erosion of the felsic upper crust over the past 300 million years. Alternatively, it could also suggest the existence of pervasive magmatic intrusion into the Appalachian crust. The Vp/Vs measurements in the Atlantic Coastal Plain increase toward the east, ranging from 1.75 to 1.82, probably indicating a gradual increase of mafic magmatic intrusion into thinner crust during the development of the passive continental margin.

Nars: Over 30 Years of Seismology

NASA Astrophysics Data System (ADS)

Paulssen, H.

2014-12-01

It is fair to say that modern seismology steadily evolved from a handful key initiatives and innovations dating back to the early 1980s. (1) The transition from non-mobile, narrow band sensors with analogue recording (pre-1980s) to portable, broadband sensors with digital recorders paved the way to flexible deployments, enabling various array and regional studies with the same instrumentation. Here I mention just two initiatives: NARS, which was the first digital, mobile network of broadband stations deployed in western Europe (1983-1987), and USarray (2003- ), which is the biggest program of recent times. Presently, innovative data acquisition systems for the oceans are underway and they will allow future imaging of the "inaccessible" parts of the Earth. (2) In the 1980s seismological data centers were set up to facilitate data archiving and distribution. Since then, open data exchange (not a matter of course) and easy data retrieval have become standard. The impact of this has been phenomenal: most observational studies efficiently retrieve data from these main seismological data centers and the archived seismograms are used for various types of studies, carried out by different persons and groups. (3) Seismic tomography changed the face of seismological research. From travel time to waveform tomography, from ray theory to finite frequency tomography: new and improved tomographic techniques greatly enhanced our images (and understanding) of the Earth's interior. (4) Many of these developments would not have been possible without young, motivated, seismologists that were educated and stimulated by insightful supervisors. One person has had a major impact on all these fields. NARS in the title stands for Nolet greatly Advanced Research in Seismology.

PBO Borehole Strainmeters and Pore Pressure Sensors: Recording Hydrological Strain Signals

NASA Astrophysics Data System (ADS)

Gottlieb, M. H.; Hodgkinson, K. M.; Mencin, D.; Henderson, D. B.; Johnson, W.; Van Boskirk, E.; Pyatt, C.; Mattioli, G. S.

2017-12-01

UNAVCO operates a network of 75 borehole strainmeters along the west coast of the United States and Vancouver Island, Canada as part of the Plate Boundary Observatory (PBO), the geodetic component of the NSF-funded Earthscope program. Borehole strainmeters are designed to detect variations in the strain field at the nanostrain level and can easily detect transient strains caused by aseismic creep events, Episodic Tremor and Slip (ETS) events and seismically induced co- and post-seimic signals. In 2016, one strainmeter was installed in an Oklahoma oil field to characterize in-situ deformation during CO2 injection. Twenty-three strainmeter sites also have pore pressure sensors to measure fluctuations in groundwater pressure. Both the strainmeter network and the pore pressure sensors provide unique data against which those using water-level measurements, GPS time-series or InSAR data can compare possible subsidence signals caused by groundwater withdrawal or fluid re-injection. Operating for 12 years, the PBO strainmeter and pore pressure network provides a long-term, continuous, 1-sps record of deformation. PBO deploys GTSM21 tensor strainmeters from GTSM Technologies, which consist of four horizontal strain gauges stacked vertically, at different orientations, within a single 2 m-long instrument. The strainmeters are typically installed at depths of 200 to 250 m and grouted into the bottom of 15 cm diameter boreholes. The pore pressure sensors are Digiquartz Depth Sensors from Paros Scientific. These sensors are installed in 2" PVC, sampling groundwater through a screened section 15 m above the co-located strainmeter. These sensors are also recording at 1-sps with a resolution in the hundredths of hPa. High-rate local barometric pressure data and low-rate rainfall data also available at all locations. PBO Strainmeter and pore pressure data are available in SEED, SAC-ASCII and time-stamped ASCII format from the IRIS Data Managements Center. Strainmeter data are available at 2-hour latency while the pore pressure data are available in real-time. Links for data access, instrument and borehole information and station histories are available from UNAVCO's Borehole Data web page (https://www.unavco.org/data/strain-seismic/bsm-data/bsm-data.html ).

Tectonic Tremor along the San Jacinto Fault Zone near Anza, California

NASA Astrophysics Data System (ADS)

Brown, J. R.

2013-12-01

In several tectonic settings where it is observed, low frequency tremor is proven as a useful tool to probe slow fault slip at depth (e.g., southwest Japan, Cascadia, Parkfield). However, tremor is difficult to detect due to its long durations and low amplitudes close to the noise band. This is particularly true in southern California where cultural noise sources are both spatially and temporally pervasive. Visually scanning continuous seismic recordings of the Southern California Seismic Network from 2001-2011 we find three pervasive occurrences of tremor: fall 2001, summer 2005 and summer 2010. In this presentation we focus on our analysis of the summer 2010 tremors on account of the enhanced instrumentation from the EarthScope Plate Boundary Observatory. During summer 2010 we detect ~240 hours of tremor-like signals in vicinity of the San Jacinto fault zone (SJFZ) near Anza. Visual inspection of continuous recordings up to 100 km northeast and southwest of the SJFZ do not record tremor-like signals indicating the source is both weak and local. Tremor is discriminated from other noise sources by calculating their spectral shapes to assure the signals are distinct from local noise sources and earthquakes. Similar to tremor spectra in other settings, the tremor signals in vicinity of the SJFZ are spectrally flat up to 9 Hz. In order to characterize the tremor source, we employ a combination of running autocorrelation and matched-filter techniques to detect and locate low frequency earthquakes (LFE) along the SJFZ one hour at a time. The autocorrelation of the north and vertical components of 14 stations detects over 13500 LFEs. We identify S-wave arrivals using the cross-correlation of 6 s windows for event pairs using the north component. Preliminary analysis of S-waves reveals a localized swarm of LFE epicenters extending 5 to 10 km SE of the Anza Gap with a horizontal error of +/- 4 km. Tremor depths are poorly constrained due to the lack of clear P-wave arrivals. The LFE epicenters reveal a zone of slow slip activity to the SE of the Anza Gap during early summer of 2010.

Magnetotelluric imaging of the subducting slab in Cascadia with constraints from seismology

NASA Astrophysics Data System (ADS)

Yang, B.; Egbert, G. D.; Kelbert, A.; Humphreys, E.

2015-12-01

We present results from three-dimensional (3D) inversion of long-period magnetotelluric (MT) data from Cascadia, using seismological constraints on plate geometry and back-arc structure, to refine 3D images of electrical resistivity across this subduction zone. For this study we employed the impedances and vertical transfer functions from 144 sites from the EarthScope Transportable Array, along with data from previous higher density MT profiles from Cascadia (EMSLAB, CAFE-MT etc.). Morphological parameters for the subducting Juan de Fuca and Gorda plates (e.g. upper boundary and thickness) were extracted from McCrory et al (2012) and Schmandt and Humphreys (2010) seismological models and used to define a resistive subducting slab structure in 3D. This was then either used as a prior model, or fixed (both resistivity and geometry) during the MT inversion. By imposing constraints on the geometry of the slab (which is otherwise imaged as an amorphous broad resistive zone) we improve recovery and resolution of subduction related conductivity features. The constrained inversions also allowed us to test sensitivity of the MT data to variants on slab geometry, such as the proposed slab "tear" near the Oregon-Washington border suggested by some seismic tomography models, and to explore consistency of the MT data with seismic models, which suggest segmentation of back-arc upwelling. Three zones of substantially reduced resistivity were found, all exhibiting significant along-strike variability. In the forearc, an N-S stripe of high conductivity (10 ohm-m or less) was found just above the plate interface, near the tip of the mantle wedge. This conductive feature is spatially coincident with mapped locations of episodic tremor and slip, and likely represents aqueous fluids associated with slab dehydration. To the east, a second, clearly separated, N-S elongate zone of similarly high conductivity occurs in the mid-lower crust and upper mantle beneath the modern arc, again likely representing fluids, and in some cases melt. Finally, in the back-arc a broader, and generally more subdued (20-30 ohm-m), zone of reduced resistivity occurs in the North American mantle above the plate interface.

Real-time and rapid GNSS solutions from the M8.2 September 2017 Tehuantepec Earthquake and implications for Earthquake and Tsunami Early Warning Systems

NASA Astrophysics Data System (ADS)

Mencin, D.; Hodgkinson, K. M.; Mattioli, G. S.

2017-12-01

In support of hazard research and Earthquake Early Warning (EEW) Systems UNAVCO operates approximately 800 RT-GNSS stations throughout western North America and Alaska (EarthScope Plate Boundary Observatory), Mexico (TLALOCNet), and the pan-Caribbean region (COCONet). Our system produces and distributes raw data (BINEX and RTCM3) and real-time Precise Point Positions via the Trimble PIVOT Platform (RTX). The 2017-09-08 earthquake M8.2 located 98 km SSW of Tres Picos, Mexico is the first great earthquake to occur within the UNAVCO RT-GNSS footprint, which allows for a rigorous analysis of our dynamic and static processing methods. The need for rapid geodetic solutions ranges from seconds (EEW systems) to several minutes (Tsunami Warning and NEIC moment tensor and finite fault models). Here, we compare and quantify the relative processing strategies for producing static offsets, moment tensors and geodetically determined finite fault models using data recorded during this event. We also compare the geodetic solutions with the USGS NEIC seismically derived moment tensors and finite fault models, including displacement waveforms generated from these models. We define kinematic post-processed solutions from GIPSY-OASISII (v6.4) with final orbits and clocks as a "best" case reference to evaluate the performance of our different processing strategies. We find that static displacements of a few centimeters or less are difficult to resolve in the real-time GNSS position estimates. The standard daily 24-hour solutions provide the highest-quality data-set to determine coseismic offsets, but these solutions are delayed by at least 48 hours after the event. Dynamic displacements, estimated in real-time, however, show reasonable agreement with final, post-processed position estimates, and while individual position estimates have large errors, the real-time solutions offer an excellent operational option for EEW systems, including the use of estimated peak-ground displacements or directly inverting for finite-fault solutions. In the near-field, we find that the geodetically-derived moment tensors and finite fault models differ significantly with seismically-derived models, highlighting the utility of using geodetic data in hazard applications.

Deformation Along the Rio Grande Rift: Investigating the Spatial and Temporal Distribution of Strain Using GPS

NASA Astrophysics Data System (ADS)

Murray, K. D.; Murray, M. H.; Sheehan, A. F.; Nerem, R. S.

2014-12-01

Low velocity (<1 mm/yr) extensional environments, such as the Rio Grande rift (RGR) in Colorado and New Mexico, are complex but can provide insights into continental dynamics, tectonic processes, and seismic hazards. We use eight years of measurements from 26 continuous GPS stations across the RGR installed as part of a collaborative EarthScope experiment. We combine this data with regional Plate Boundary Observatory (PBO) and National Geodetic Survey (NGS) CORS GPS stations, and survey-mode data collected on NGS benchmarks to investigate how deformation is distributed across a broad area from the Great Plains to the Colorado Plateau. The data from over 150 stations are processed using GAMIT/GLOBK, and time series, velocities, strain rates are estimated with respect to realizations of a stable North America reference frame, such as NA12. This study extends our previous analysis, based on 4 years of data, which found an approximately uniform 1.2 nanostrain/yr east-west extensional strain rate across the entire region that was not concentrated on the narrow surface expression of the rift. We expand on this previous work by using a denser network of GPS stations and analyzing longer time series, which reduce horizontal velocity uncertainties to approximately 0.15 mm/yr. We also improve the accuracy of the estimated velocity uncertainties by robustly characterizing time-correlated noise. The noise models indicate that both power-law and flicker noise are present in the time series along with white noise. On average, power law noise constitutes about 90% of the total noise in the vertical component and 60% in the horizontal components for the RGR sites. We use the time series, and velocity and strain-rate estimates to constrain spatial and temporal variations in the deformation field in order to locate possible regions of strain localization and detect transient deformation signals, and to address some of the kinematic and dynamic issues raised by the observation that a broad, low seismic velocity zone underlies the narrow geologic surface expression of the RGR defined by normal fault bounded basins.

OBSIP: An Evolving Facility for the Future of Geoscience

NASA Astrophysics Data System (ADS)

Evers, B.; Lodewyk, J. A.

2013-12-01

The Ocean Bottom Seismograph Instrument Pool 'OBSIP' was founded in 1999 as a National Science Foundation (NSF) sponsored instrument facility that provides ocean bottom seismometers and technical support for research in the areas of marine geology, seismology, and geodynamics. OBSIP provides both short period instruments (for active source seismic refraction studies) and long period instruments (for long term passive experiments). OBSIP is comprised of three Institutional Instrument Contributors - Lamont Doherty Earth Observatory (LDEO), Scripps Institution of Oceanography (SIO), and Woods Hole Oceanographic Institution (WHOI), each of whom contribute instruments and technical support to the pool. In 2012, NSF funded the Incorporated Research Institutions of Seismology (IRIS) to develop an OBSIP Management Office. Through the management office, IRIS will bring is extensive experience in managing facilities (PASSCAL instrument center), supporting large research experiments (Earthscope), and providing high quality data through the DMC to OBSIP. In the past year, OBSIP has provided instruments for eight experiments and supported over 20 research cruises recovering and/or deploying instruments. The most extensive OBSIP experiment in the past few years has been the Cascadia Initiative. The Cascadia Initiative is an onshore/offshore seismic and geodetic experiment deployed in the Pacific Northwest to study questions surrounding the evolution of the Juan de Fuca plate and the Gorda plate. As part of the American Recovery and Reinvestment Act, OBSIP IIC's built 60 new ocean bottom seismometers. Both LDEO and SIO designed new seismometer packages to withstand trawling by local fisherman for deployment in shallow areas. The Cascadia Initiative has required close cooperation between the OBSIP, the Deep Submergence Facility, the University National Oceanographic Laboratory System (who coordinates ship schedules for the cruises), and the Cascadia Initiative Expedition Team. At the recent OBSIP Workshop, members from the scientific community met to share scientific results and determine how OBS instrumentation can better serve the scientific community. The OBSIP Management Office is developing a comprehensive Data Quality Plan that includes all steps of the data collection process, from instrument design to quality controlling data after it is uploaded to the Data Management Center. OBSIP continues to evolve as it works to better serve the scientific community and the public.

Surface-wave amplitude analysis for array data with non-linear waveform fitting: Toward high-resolution attenuation models of the upper mantle

NASA Astrophysics Data System (ADS)

Hamada, K.; Yoshizawa, K.

2013-12-01

Anelastic attenuation of seismic waves provides us with valuable information on temperature and water content in the Earth's mantle. While seismic velocity models have been investigated by many researchers, anelastic attenuation (or Q) models have yet to be investigated in detail mainly due to the intrinsic difficulties and uncertainties in the amplitude analysis of observed seismic waveforms. To increase the horizontal resolution of surface wave attenuation models on a regional scale, we have developed a new method of fully non-linear waveform fitting to measure inter-station phase velocities and amplitude ratios simultaneously, using the Neighborhood Algorithm (NA) as a global optimizer. Model parameter space (perturbations of phase speed and amplitude ratio) is explored to fit two observed waveforms on a common great-circle path by perturbing both phase and amplitude of the fundamental-mode surface waves. This method has been applied to observed waveform data of the USArray from 2007 to 2008, and a large-number of inter-station amplitude and phase speed data are corrected in a period range from 20 to 200 seconds. We have constructed preliminary phase speed and attenuation models using the observed phase and amplitude data, with careful considerations of the effects of elastic focusing and station correction factors for amplitude data. The phase velocity models indicate good correlation with the conventional tomographic results in North America on a large-scale; e.g., significant slow velocity anomaly in volcanic regions in the western United States. The preliminary results of surface-wave attenuation achieved a better variance reduction when the amplitude data are inverted for attenuation models in conjunction with corrections for receiver factors. We have also taken into account the amplitude correction for elastic focusing based on a geometrical ray theory, but its effects on the final model is somewhat limited and our attenuation model show anti-correlation with the phase velocity models; i.e., lower attenuation is found in slower velocity areas that cannot readily be explained by the temperature effects alone. Some former global scale studies (e.g., Dalton et al., JGR, 2006) indicated that the ray-theoretical focusing corrections on amplitude data tend to eliminate such anti-correlation of phase speed and attenuation, but this seems not to work sufficiently well for our regional scale model, which is affected by stronger velocity gradient relative to global-scale models. Thus, the estimated elastic focusing effects based on ray theory may be underestimated in our regional-scale studies. More rigorous ways to estimate the focusing corrections as well as data selection criteria for amplitude measurements are required to achieve a high-resolution attenuation models on regional scales in the future.

3-D Inversion of the MT EarthScope Data, Collected Over the East Central United States

NASA Astrophysics Data System (ADS)

Gribenko, A. V.; Zhdanov, M. S.

2017-12-01

The magnetotelluric (MT) data collected as a part of the EarthScope project provided a unique opportunity to study the conductivity structure of the deep interior of the North American continent. Besides the scientific value of the recovered subsurface models, the data also allowed inversion practitioners to test the robustness of their algorithms applied to regional long-period data. In this paper, we present the results of MT inversion of a subset of the second footprint of the MT data collection covering the East Central United States. Our inversion algorithm implements simultaneous inversion of the full MT impedance data both for the 3-D conductivity distribution and for the distortion matrix. The distortion matrix provides the means to account for the effect of the near-surface geoelectrical inhomogeneities on the MT data. The long-period data do not have the resolution for the small near-surface conductivity anomalies, which makes an application of the distortion matrix especially appropriate. The determined conductivity model of the region agrees well with the known geologic and tectonic features of the East Central United States. The conductivity anomalies recovered by our inversion indicate a possible presence of the hot spot track in the area.

Western US Seismic Observations Viewed Through Lead Isotope Maps

NASA Astrophysics Data System (ADS)

Bouchet, R. A.; Blichert-Toft, J.; Levander, A.; Reid, M. R.; Albarede, F.

2013-12-01

To shed light on the nature and history of the different geological units identified by the seismic models that have come from USArray in the western US, we compiled literature Pb isotope compositions of ores (n=1200), K-feldspars from granites (n=400), and felsic plutonic rocks (n=1300), data that for most part were not in the NAVDAT database. We complemented this compilation by analyzing the Pb isotope compositions of K-feldspars (76) and whole-rocks (6) of felsic xenoliths and felsic plutonic rocks from the Colorado Plateau (CP). The raw Pb isotope abundances for the complete data set were converted into three independent, geologically informative parameters in the form of the model age T (time of last U/Pb fractionation) and the two chemical ratios 238U/204Pb (μ) and 232Th/238U (κ). These parameters were then imaged on isotopic maps of the western US using 0.5°×0.5° grid-cell averaging for μ and κ and a 0.5°×0.5° grid-cell maximum after removing the 2.5% highest values (outliers) for T. Comparing these chemical maps to seismic maps of tomographic anomalies [1] and Moho and LAB depths determined from receiver functions [2] leads to the following observations: (i) Pb model ages: they match geological ages mostly where the continental mantle is cold and the Moho is deep. Elsewhere, Pb model ages are younger than geological ages. We interpret this feature as the chronological expression of a delayed cooling of deep crustal layers below the closure temperature (˜550-700°C) of Pb in K-feldspar, the major host of this element in the crust [3] or of age resetting by orogenic activity. (ii) While U/Pb (μ) does not vary systematically with other geochemical or seismic data, high Th/U (κ) values are usually observed where Vp/Vs is also high, as in the Snake River basin and central Colorado. High kappa values also form a 'ridge' trending south from northwestern Utah through the Basin and Range into the Mojave-Yavapai block. High-κ areas may reflect the presence of deep-seated rocks exhumed as a result of regional extension or collapse. They may also reveal the presence of channels of flowing crust originating either beneath the CP and spreading north, or along the track of the Yellowstone hotspot track and spreading south [4]. [1] Schmandt, B., and E. Humphreys (2010), Complex subduction and small-scale convection revealed by body-wave tomography of the western United States upper mantle, Earth Planet. Sci. Lett., 297, 435-445. [2] Levander, A., and M.S. Miller (2012), Evolutionary aspects of the lithosphere discontinuity structure in the western U.S., G-cubed, 13, 1-22. [3] Cherniak, D.J. (1995), Diffusion of lead in plagioclase and K-feldspar: an investigation using Rutherford Backscattering and Resonant Nuclear Reaction Analysis, Contrib. Mineral. Petrol., 120, 358-371. [4] Yuan, H., K. Dueker, and J. Stachnik (2010), Crustal structure and thickness along the Yellowstone hot spot track: evidence for lower crustal outflow from beneath the eastern Snake River Plain, G-cubed, 11, 1-14.

Short-period surface-wave phase velocities across the conterminous United States

NASA Astrophysics Data System (ADS)

Ekström, G.

2017-09-01

Surface-wave phase-velocity maps for the full footprint of the USArray Transportable Array (TA) across the conterminous United States are developed and tested. Three-component, long-period continuous seismograms recorded on more than 1800 seismometers, most of which were deployed for 18 months or longer, are processed using a noise cross-correlation technique to derive inter-station Love and Rayleigh dispersion curves at periods between 5 and 40 s. The phase-velocity measurements are quality controlled using an automated algorithm and then used in inversions for Love and Rayleigh phase-velocity models at discrete periods on a 0.25°-by-0.25° pixel grid. The robustness of the results is examined using comparisons of maps derived from subsets of the data. A winter-summer division of the cross-correlation data results in small model differences, indicating relatively minor sensitivity of the results to seasonal variations in the distribution of noise sources. Division of the dispersion data based on inter-station azimuth does not result in geographically coherent model differences, suggesting that azimuthal anisotropy at the regional scale is weak compared with variations in isotropic velocities and does not substantially influence the results for isotropic velocities. The phase-velocity maps and dispersion measurements are documented and made available as data products of the 10-year-long USArray TA deployment.

Sutures and an Anomalous Deep Lithospheric Electrical Resistor in the Southeastern United States as Revealed by EarthScope Magnetotelluric Data

NASA Astrophysics Data System (ADS)

Murphy, B. S.; Egbert, G. D.

2016-12-01

We use newly acquired long-period magnetotelluric data to examine lithospheric structure beneath the modern Southern Appalachian Mountains and the adjacent Piedmont. The New York-Alabama Lineament is clearly visible both in inverse models and in the data themselves as a major Appalachian-parallel, mid- to lower-crustal conductive feature. This observation supports geologically-based interpretations of the NY-AL Lineament as a major Grenville suture. We also discern several other suture zones in our inverse models, including the Central Piedmont Suture. Interestingly, we do not observe any geoelectric signature of the Suwannee Suture. Most strikingly, we find a zone of exceptionally high resistivity (>1000 μm) that extends to a depth of more than 200 km beneath the modern Piedmont. This resistive block abuts more conductive lithosphere ( 100 μm, as would be expected for Phanerozoic lithosphere) to the northwest. The boundary between these two distinct domains coincides with the modern Appalachian topographic escarpment to within our resolution. The high resistivity values would seem to require completely dry, highly depleted lithosphere at anomalously cold temperatures; however, corresponding seismically fast lithospheric mantle that would be expected for such a structure has not been observed in any previous studies. The exact nature of this feature therefore remains uncertain at present. Regardless, as it is a persistent feature in inversions and it is also readily apparent in the impedance data, this geoelectric structure likely holds important implications for the past, present, and future tectonic evolution of the Southeastern United States.

ADVANCED WAVEFORM SIMULATION FOR SEISMIC MONITORING EVENTS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Helmberger, Donald V.; Tromp, Jeroen; Rodgers, Arthur J.

2008-10-17

This quarter, we have focused on several tasks: (1) Building a high-quality catalog of earthquake source parameters for the Middle East and East Asia. In East Asia, we computed source parameters using the CAP method for a set of events studied by Herrman et al., (MRR, 2006) using a complete waveform technique. Results indicated excellent agreement with the moment magnitudes in the range 3.5 -5.5. Below magnitude 3.5 the scatter increases. For events with more than 2-3 observations at different azimuths, we found good agreement of focal mechanisms. Depths were generally consistent, although differences of up to 10 km weremore » found. These results suggest that CAP modeling provides estimates of source parameters at least as reliable as complete waveform modeling techniques. However, East Asia and the Yellow Sea Korean Paraplatform (YSKP) region studied are relatively laterally homogeneous and may not benefit from the CAP method’s flexibility to shift waveform segments to account for path-dependent model errors. A more challenging region to study is the Middle East where strong variations in sedimentary basin, crustal thickness and crustal and mantle seismic velocities greatly impact regional wave propagation. We applied the CAP method to a set of events in and around Iran and found good agreement between estimated focal mechanisms and those reported by the Global Centroid Moment Tensor (CMT) catalog. We found a possible bias in the moment magnitudes that may be due to the thick low-velocity crust in the Iranian Plateau. (2) Testing Methods on a Lifetime Regional Data Set. In particular, the recent 2/21/08 Nevada Event and Aftershock Sequence occurred in the middle of USArray, producing over a thousand records per event. The tectonic setting is quite similar to Central Iran and thus provides an excellent testbed for CAP+ at ranges out to 10°, including extensive observations of crustal thinning and thickening and various Pnl complexities. Broadband modeling in 1D, 2D, and 3D will be presented. (3) Shallow Crustal Structure and Sparse Network Source Inversions for Southern California. We conducted a detailed test of a recently developed technique, CAPloc, in recovering source parameters including location and depth based on tomographic maps. We tested two-station solutions against 160 well determined events which worked well except for paths crossing deep basins and along mountain ridges.« less

Rupture process of the 2013 Okhotsk deep mega earthquake from iterative backprojection and compress sensing methods

NASA Astrophysics Data System (ADS)

Qin, W.; Yin, J.; Yao, H.

2013-12-01

On May 24th 2013 a Mw 8.3 normal faulting earthquake occurred at a depth of approximately 600 km beneath the sea of Okhotsk, Russia. It is a rare mega earthquake that ever occurred at such a great depth. We use the time-domain iterative backprojection (IBP) method [1] and also the frequency-domain compressive sensing (CS) technique[2] to investigate the rupture process and energy radiation of this mega earthquake. We currently use the teleseismic P-wave data from about 350 stations of USArray. IBP is an improved method of the traditional backprojection method, which more accurately locates subevents (energy burst) during earthquake rupture and determines the rupture speeds. The total rupture duration of this earthquake is about 35 s with a nearly N-S rupture direction. We find that the rupture is bilateral in the beginning 15 seconds with slow rupture speeds: about 2.5km/s for the northward rupture and about 2 km/s for the southward rupture. After that, the northward rupture stopped while the rupture towards south continued. The average southward rupture speed between 20-35 s is approximately 5 km/s, lower than the shear wave speed (about 5.5 km/s) at the hypocenter depth. The total rupture length is about 140km, in a nearly N-S direction, with a southward rupture length about 100 km and a northward rupture length about 40 km. We also use the CS method, a sparse source inversion technique, to study the frequency-dependent seismic radiation of this mega earthquake. We observe clear along-strike frequency dependence of the spatial and temporal distribution of seismic radiation and rupture process. The results from both methods are generally similar. In the next step, we'll use data from dense arrays in southwest China and also global stations for further analysis in order to more comprehensively study the rupture process of this deep mega earthquake. Reference [1] Yao H, Shearer P M, Gerstoft P. Subevent location and rupture imaging using iterative backprojection for the 2011 Tohoku Mw 9.0 earthquake. Geophysical Journal International, 2012, 190(2): 1152-1168. [2]Yao H, Gerstoft P, Shearer P M, et al. Compressive sensing of the Tohoku-Oki Mw 9.0 earthquake: Frequency-dependent rupture modes. Geophysical Research Letters, 2011, 38(20).

EarthScope Plate Boundary Observatory Data in the College Classroom (Invited)

NASA Astrophysics Data System (ADS)

Eriksson, S. C.; Olds, S. E.

2009-12-01

The Plate Boundary Observatory (PBO) is the geodetic component of the EarthScope project, designed to study the 3-D strain field across the active boundary zone between the Pacific and North American tectonics plates in the western United States. All PBO data are freely available to scientific and educational communities and have been incorporated into a variety of activities for college and university classrooms. UNAVCO Education and Outreach program staff have worked closely with faculty users, scientific researchers, and facility staff to create materials that are scientifically and technically accurate as well as useful to the classroom user. Availability of processed GPS data is not new to the geoscience community. However, PBO data staff have worked with education staff to deliver data that are readily accessible to educators. The UNAVCO Data for Educators webpage, incorporating an embedded Google Map with PBO GPS locations and providing current GPS time series plots and downloadable data, extends and updates the datasets available to our community. Google Earth allows the visualization GPS data with other types of datasets, e.g. LiDAR, while maintaining the self-contained and easy-to-use interface of UNAVCO’s Jules Verne Voyager map tools, which have multiple sets of geological and geophysical data. Curricular materials provide scaffolds for using EarthScope data in a variety of forms for different learning goals. Simple visualization of earthquake epicenters and locations of volcanoes can be used with velocity vectors to make simple deductions of plate boundary behaviors. Readily available time series plots provide opportunities for additional science skills, and there are web and paper-based support materials for downloading data, manipulating tables, and using plotting programs for processed GPS data. Scientists have provided contextual materials to explore the importance of these data in interpreting the structure and dynamics of the Earth. These data and their scientific context are now incorporated into the Active Earth Display developed by IRIS. Formal and informal evaluations during the past five years have provided useful data for revision and on-line implementation.

Rapid Regional Centroid Solutions

NASA Astrophysics Data System (ADS)

Wei, S.; Zhan, Z.; Luo, Y.; Ni, S.; Chen, Y.; Helmberger, D. V.

2009-12-01

The 2008 Wells Nevada Earthquake was recorded by 164 broadband USArray stations within a distance of 550km (5 degrees) with all azimuths uniformly sampled. To establish the source parameters, we applied the Cut and Paste (CAP) code to all the stations to obtain a mechanism (strike/dip/rake=35/41/-85) at a depth of 9km and Mw=5.9. Surface wave shifts range from -8s to 8s which are in good agreement with ambient seismic noise (ASN) predictions. Here we use this data set to test the accuracy of the number of stations needed to obtain adequate solutions (position of the compressional and tension axis) for mechanism. The stations were chosen at random where combinations of Pnl and surface waves were used to establish mechanism and depth. If the event is bracketed by two stations, we obtain an accurate magnitude with good solutions about 80% of the trials. Complete solutions from four stations or Pnl from 10 stations prove reliable in nearly all situations. We also explore the use of this dataset in locating the event using a combination of surface wave travel times and/or the full waveform inversion (CAPloc) that uses the CAP shifts to refine locations. If the mechanism is known (fixed) only a few stations is needed to locate an event to within 5km if date is available at less than 150km. In contrast, surface wave travel times (calibrated to within one second) produce amazing accurate locations with only 6 stations reasonably distributed. It appears this approach is easily automated as suggested by Scrivner and Helmberger (1995) who discussed travel times of Pnl and surface waves and the evolving of source accuracy as the various phases arrive.

Improved Seismic Images of the Pacific Northwest Interior, With a Focus on the Region of the Columbia River Flood Basalts and Central Idaho

NASA Astrophysics Data System (ADS)

Stanciu, A. C.; Humphreys, E.; Clayton, R. W.

2017-12-01

We construct a P-wave model of the upper mantle based on new and previously acquired data from the USArray-TA stations and regional deployments, including the HLP, ID-OR, and the currently recording Wallowa stations. Our teleseismic arrival times are corrected for crustal structure (based on surface wave, receiver function, and controlled-source models from the region). Our modeling incorporates 3-D ray tracing and several simple considerations of radial anisotropy on travel time. As imaged previously, we find high P-wave velocity anomalies located beneath the Wallowa Mountains and beneath the Idaho Batholith in central west Idaho. Our improved imaging finds that these two anomalies are located down to 350 km depth, and are clearly separated from one another and from a shallower fast anomaly in the uppermost mantle beneath the westernmost Snake River Plain. Our preferred interpretation includes a combination of delamination and slab fragments in this region. As fast (and presumably cool) structures, these upper-mantle anomalies are thought to have a lithospheric origin. The anomaly beneath central Idaho is interpreted as the leading edge of the Farallon slab associated with the accretion of Siletzia terrane to North America. This anomaly may include some North American lithosphere that delaminated from the Laramide-thickened lithospheric mantle, perhaps related to Challis magmatism. The Wallowa anomaly is likely to represent Farallon lithosphere that delaminated during the Columbia River flood basalt event. The small anomaly between the two deeper fast anomalies, occurring at depths above 150km, could represent an isolated lithospheric fragment or a structure created by the Columbia River flood basalt event.

Recent Instrumentation Developments in the Global Seismographic Network (GSN)

NASA Astrophysics Data System (ADS)

Hafner, K.; Davis, J. P.; Wilson, D.

2016-12-01

One of the challenges facing the GSN is continuing to provide robust, uniform high-quality, very broadband, high-dynamic range recordings of ground motion data as the original primary seismometers age. Recently the GSN has been upgrading all stations with the next generation of digital data acquisition systems (DASs), which has significantly increased the station data availability. In 2012, the Department of Energy received an additional $5.7M to support GSN refurbishment. The funds were transferred to the USGS via a 5-year interagency agreement and have been used for developing the next generation of very broadband (VBB) sensors. The USGS Albuquerque Seismic Laboratory (ASL) received the first prototype of a very broadband borehole sensor (Streckeisen STS-6A) in November 2015. Initial testing showed this prototype met all the required sensor specifications. Three pre-production sensors are scheduled to arrive by late August 2016. We will present the results of testing these devices, as well as an update on other recent VBB sensor developments (Trillium T360) and how they compare to the performance of the STS-1 and other available sensors. Recent work at ASL and the USArray Transportable Array has shown that installing sensors in shallow postholes up to 10 meters deep can lead to significant improvement in data quality. The GSN is investigating the potential of installing borehole sensors at some GSN stations where the STS-1 has shown significant susceptibility to pier tilt, temperature instability, or cultural noise. The GSN is also broadening the types of sensors deployed at GSN stations. After initial testing at ASL and UCSD's Pinyon Flat test site, the first infrasound sensor deployment will take place in Fall 2016. We will present the results of these tests and descriptions of the initial deployment.

Mermaid Seismometry in the Oceans: What Can We Resolve and How Far Will We Go?

NASA Astrophysics Data System (ADS)

Nolet, G.; Sukhovich, A.; Bonnieux, S.; Hello, Y.; Simons, F. J.; Irisson, J. O.

2015-12-01

Two years of test runs in the Mediterranean and the Indian Ocean as well as two (still ongoing) tomographic experiments in the Ligurian Sea and near the Galapagos Islands, allow us to evaluate the potential for an array of floating seismographs to fill the data gap for seismic tomography posed by the oceans.P-wave onsets obtained by three MERMAIDs in the Ligurian Sea have been validated by inverting them together with onsets measured in the same area from an OBS experiment as well as with nearby land stations. Judging fromthe posteriori misfits, an average accuracy of 0.4 seconds was obtained despite the presence of some outliers. Using this accuracy estimate, current detection rates as a function of distance and magnitude, and observed trajectories of floats in the oceanographic ARGO program, we have modelled the data yield expected from a global array of MERMAIDs operating for five years (a new, second generation, MERMAID has a longevity in excess of five years). With 300 MERMAIDs, we expect to obtain 102,080 onset times, which allows an almost perfect geographical coverage. This rises to 341,607 in a simulation with 1000 MERMAIDs, which is much less than the 1,567,829 selected over the same period from the ISC catalogue. However, inverting these together in a checkerboard test (Figure) shows that we can resolve anomalies of size as small as 300 km almost perfectly in most of the lower mantle, with the exception of the mantle under polar regions, Africa and the South Atlantic. Inverting the ISC data alone leaves the oceanic domain unresolved at this length scale.The cost of such a MARISCOPE array (about $30M) compares favourably with the cost of the US-Array deployment.

MERMAID seismometry in the oceans: resolving the detail of geodynamic processes

NASA Astrophysics Data System (ADS)

Nolet, Guust

2016-04-01

Two years of test runs in the Mediterranean and the Indian Ocean as well as two tomographic experiments in the Ligurian Sea and near the Galapagos Islands, allow us to evaluate the potential for an array of floating seismographs to fill the data gap for seismic tomography posed by the oceans. P-wave onsets obtained by three MERMAIDs in the Ligurian Sea have been validated by inverting them together with onsets measured in the same area from an OBS experiment as well as with nearby land stations. Judging from the posteriori misfits, an average accuracy of 0.4 seconds was obtained despite the presence of some outliers. Using this accuracy estimate, current detection rates as a function of distance and magnitude, and observed trajectories of floats in the oceanographic ARGO program, we have modelled the data yield expected from a global array of MERMAIDs operating for five years (a new, second generation, MERMAID has a longevity in excess of five years). With 300 MERMAIDs, we expect to obtain 102,080 onset times, which allows an almost perfect geographical coverage. This rises to 341,607 in a simulation with 1000 MERMAIDs, which is much less than the 1,567,829 delays selected over the same period from the ISC catalogue. However, inverting these together in a checkerboard test shows that we can resolve anomalies of size as small as 300 km almost perfectly in most of the lower mantle, with the exception of the mantle under polar regions, Africa and the South Atlantic. Inverting the ISC data alone leaves the oceanic domain unresolved at this length scale. The cost of such a MARISCOPE array (about 30M) compares favourably with the cost of the US-Array deployment.

Building the European Seismological Research Infrastructure: results from 4 years NERIES EC project

NASA Astrophysics Data System (ADS)

van Eck, T.; Giardini, D.

2010-12-01

The EC Research Infrastructure (RI) project, Network of Research Infrastructures for European Seismology (NERIES), implemented a comprehensive European integrated RI for earthquake seismological data that is scalable and sustainable. NERIES opened a significant amount of additional seismological data, integrated different distributed data archives, implemented and produced advanced analysis tools and advanced software packages and tools. A single seismic data portal provides a single access point and overview for European seismological data available for the earth science research community. Additional data access tools and sites have been implemented to meet user and robustness requirements, notably those at the EMSC and ORFEUS. The datasets compiled in NERIES and available through the portal include among others: - The expanded Virtual European Broadband Seismic Network (VEBSN) with real-time access to more then 500 stations from > 53 observatories. This data is continuously monitored, quality controlled and archived in the European Integrated Distributed waveform Archive (EIDA). - A unique integration of acceleration datasets from seven networks in seven European or associated countries centrally accessible in a homogeneous format, thus forming the core comprehensive European acceleration database. Standardized parameter analysis and actual software are included in the database. - A Distributed Archive of Historical Earthquake Data (AHEAD) for research purposes, containing among others a comprehensive European Macroseismic Database and Earthquake Catalogue (1000 - 1963, M ≥5.8), including analysis tools. - Data from 3 one year OBS deployments at three sites, Atlantic, Ionian and Ligurian Sea within the general SEED format, thus creating the core integrated data base for ocean, sea and land based seismological observatories. Tools to facilitate analysis and data mining of the RI datasets are: - A comprehensive set of European seismological velocity reference model including a standardized model description with several visualisation tools currently adapted on a global scale. - An integrated approach to seismic hazard modelling and forecasting, a community accepted forecasting testing and model validation approach and the core hazard portal developed along the same technologies as the NERIES data portal. - Implemented homogeneous shakemap estimation tools at several large European observatories and a complementary new loss estimation software tool. - A comprehensive set of new techniques for geotechnical site characterization with relevant software packages documented and maintained (www.geopsy.org). - A set of software packages for data mining, data reduction, data exchange and information management in seismology as research and observatory analysis tools NERIES has a long-term impact and is coordinated with related US initiatives IRIS and EarthScope. The follow-up EC project of NERIES, NERA (2010 - 2014), is funded and will integrate the seismological and the earthquake engineering infrastructures. NERIES further provided the proof of concept for the ESFRI2008 initiative: the European Plate Observing System (EPOS). Its preparatory phase (2010 - 2014) is also funded by the EC.

Real-Time In-Situ Measurements for Earthquake Early Warning and Space-Borne Deformation Measurement Mission Support

NASA Astrophysics Data System (ADS)

Kedar, S.; Bock, Y.; Webb, F.; Clayton, R. W.; Owen, S. E.; Moore, A. W.; Yu, E.; Dong, D.; Fang, P.; Jamason, P.; Squibb, M. B.; Crowell, B. W.

2010-12-01

In situ geodetic networks for observing crustal motion have proliferated over the last two decades and are now recognized as indispensable tools in geophysical research, along side more traditional seismic networks. The 2007 National Research Council’s Decadal Survey recognizes that space-borne and in situ observations, such as Interferometric Synthetic Aperture Radar (InSAR) and ground-based continuous GPS (CGPS) are complementary in forecasting, in assessing, and in mitigating natural hazards. However, the information content and timeliness of in situ geodetic observations have not been fully exploited, particularly at higher frequencies than traditional daily CGPS position time series. Nor have scientists taken full advantage of the complementary natures of geodetic and seismic data, as well as those of space-based and in situ observations. To address these deficits we are developing real-time CGPS data products for earthquake early warning and for space-borne deformation measurement mission support. Our primary mission objective is in situ verification and validation for DESDynI, but our work is also applicable to other international missions (Sentinel 1a/1b, SAOCOM, ALOS 2). Our project is developing new capabilities to continuously observe and mitigate earthquake-related hazards (direct seismic damage, tsunamis, landslides, volcanoes) in near real-time with high spatial-temporal resolution, to improve the planning and accuracy of space-borne observations. We also are using GPS estimates of tropospheric zenith delay combined with water vapor data from weather models to generate tropospheric calibration maps for mitigating the largest source of error, atmospheric artifacts, in InSAR interferograms. These functions will be fully integrated into a Geophysical Resource Web Services and interactive GPS Explorer data portal environment being developed as part of an ongoing MEaSUREs project and NASA’s contribution to the EarthScope project. GPS Explorer, originally designed for web-based dissemination of long-term Solid Earth Science Data Records (ESDR’s) such as deformation time series, tectonic velocity vectors, and strain maps, provides the framework for seamless inclusion of the high rate data products. Detection and preliminary modeling of interesting signals by dense real-time high-rate ground networks will allow mission planners and decision makers to fully exploit the less-frequent but higher resolution InSAR observations. Fusion of in situ elements into an advanced observation system will significantly improve the scientific value of extensive surface displacement data, provide scientists with improved access to modern software tools to manipulate and model these data, increase the data’s accuracy and timeliness at higher frequencies than available from space-based observations, and increase the accuracy of space-based observations through calibration of atmospheric and other systematic errors.

The Denali Earth Science Education Project

NASA Astrophysics Data System (ADS)

Hansen, R. A.; Stachnik, J. C.; Roush, J. J.; Siemann, K.; Nixon, I.

2004-12-01

In partnership with Denali National Park and Preserve and the Denali Institute, the Alaska Earthquake Information Center (AEIC) will capitalize upon an extraordinary opportunity to raise public interest in the earth sciences. A coincidence of events has made this an ideal time for outreach to raise awareness of the solid earth processes that affect all of our lives. On November 3, 2002, a M 7.9 earthquake occurred on the Denali Fault in central Alaska, raising public consciousness of seismic activity in this state to a level unmatched since the M 9.2 "Good Friday" earthquake of 1964. Shortly after the M 7.9 event, a new public facility for scientific research and education in Alaska's national parks, the Murie Science and Learning Center, was constructed at the entrance to Denali National Park and Preserve only 43 miles from the epicenter of the Denali Fault Earthquake. The AEIC and its partners believe that these events can be combined to form a synergy for the creation of unprecedented opportunities for learning about solid earth geophysics among all segments of the public. This cooperative project will undertake the planning and development of education outreach mechanisms and products for the Murie Science and Learning Center that will serve to educate Alaska's residents and visitors about seismology, tectonics, crustal deformation, and volcanism. Through partnerships with Denali National Park and Preserve, this cooperative project will include the Denali Institute (a non-profit organization that assists the National Park Service in operating the Murie Science and Learning Center) and Alaska's Denali Borough Public School District. The AEIC will also draw upon the resources of long standing state partners; the Alaska Division of Geological & Geophysical Surveys and the Alaska Division of Homeland Security and Emergency Services. The objectives of this project are to increase public awareness and understanding of the solid earth processes that affect life in Alaska, and to provide new and innovative science curricula and teacher training for the benefit of students and teachers in Alaska and beyond. These objectives will be met by the development of learning opportunities and resources that will come together around the Murie Science and Learning Center as a focus for interpretation of EarthScope science and research results in Alaska. Project activities will take place in five areas, which are: 1) development of interactive museum displays for the Murie Science and Learning Center utilizing cutting edge technology for learning, 2) public outreach with a series of publications and Internet resources, 3) development of inquiry-based, experiential curricula for middle school students to enhance science education, 4) development of accredited teacher training workshops for science educators, and 5) the creation of opportunities for EarthScope scientists to interact with students, teachers, and the public through a series of lectures and discussions in national parks and local communities across Alaska.

Resolving mantle structure beneath the Pacific Northwest

NASA Astrophysics Data System (ADS)

Darold, A. P.; Humphreys, E.; Schmandt, B.; Gao, H.

2011-12-01

Cenozoic tectonics of the Pacific Northwest (PNW) and the associated mantle structures are remarkable, the latter revealed only recently by EarthScope seismic data. Over the last ~66 Ma this region experienced a wide range of tectonic and magmatic conditions: Laramide compression, ~75-53 Ma, involving Farallon flat-slab subduction, regional uplift, and magmatic quiescence. With the ~53 Ma accretion of Siletzia ocean lithosphere within the Columbia Embayment, westward migration of subduction beginning Cascadia, along with initiation of the Cascade volcanic arc. Within the continental interior the Laramide orogeny was quickly followed by a period of extension involving metamorphic core complexes and the associated initial ignimbrite flare-up (both in northern Washington, Idaho, and western Montana); interior magmo-tectonic activity is attributed to flat-slab removal and (to the south) slab rollback. Rotation of Siletzia created new crust on SE Oregon and, at ~16 Ma, the Columbia River Flood Basalt (CRB) eruptions renewed vigorous magmatism. We have united several EarthScope studies in the Pacific Northwest and have focused on better resolving the major mantle structures that have been discovered. We have tomographically modeled the body waves with teleseismic, finite-frequency code under the constraints of ambient noise tomography and teleseismic receiver function models of Gao et al. (2011), and teleseismic anisotropy models of Long et al. (2009) in order to resolve structures continuously from the surface to the base of the upper mantle. We now have clear imaging of two episodes of subduction: Juan De Fuca slab deeper than ~250 km is absent across much of the PNW, and it has an E-W tear located beneath northern Oregon; Farallon slab (the "Siletzia curtain") is still present, hanging vertically just inboard of the core complexes, and with a basal tear causing the structure to extend deeper (~600 km) beneath north-central Idaho than beneath south-central Idaho and northern Washington (~300 km). Lying just west of the Siletzia curtain, beneath NE Oregon, is a prominent high-velocity body centered on 250 km depth. Its nearly circular plan view corresponds with the area of intense Columbia River Basalt eruptions and with the circular topographic bull's eye centered on the recently uplifted (post CRB) Wallowa Mountains. Finally, we are investigating a very low-velocity volume of mantle present between the E-W Juan de Fuca tear and the high-velocity body beneath the Wallowa Mountains. At 250 km depth this is the strongest low-velocity anomaly beneath the western U.S. Presently we are completing resolution testing on the structures revealed through our imaging in order to resolve their structural details. These synthetic resolution tests along with the high resolution imaging of the crust and upper mantle will clarify several previously cited structures as well as strengthen our conclusions on the tectonic history and geodynamical evolution of the mantle while aiding in putting together a comprehensive story for the area.

The National Science Foundation CAREER Award: A Unique Solution to the Challenges of the Tenure Process

NASA Astrophysics Data System (ADS)

Fouch, M. J.

2011-12-01

There is a dichotomy inherent in the tenure process at most research-strong universities. Most institutions require strong performance in research production and grant acquisition, while at the same time very good to excellent teaching performance. However, in the first several years of the tenure process, many new faculty spend most of their time preparing lectures for new classes and writing grant proposals, leaving little time to forge new directions and define their individual paths in their research, which, somewhat ironically, is the primary factor by which tenure is either granted or denied. The CAREER grant is a unique solution to this problem, as it enables beginning faculty members to directly thread their research into their teaching, and vice versa. My CAREER award, the first granted by the (at the time) fledgling EarthScope Science program at NSF, enabled me to bring EarthScope data and science directly into the classroom. One cadre of efforts was a focus on software development, which is a critical roadblock in geophysics for students who do not have extensive experience with Unix-based coding. For example, Kevin Eagar developed the MATLAB-based FuncLab software system that enables one to quickly and efficiently analyze receiver functions, allowing one to image layers within Earth's interior, such as the crust-mantle boundary. This system is now publically available at http://geophysics.asu.edu/funclab. At Arizona State University, 5 undergraduate students and 2 graduate students have already used this software package to produce publishable scientific results over the past 2 years, enabling them to experience research firsthand and learn a range of key research skills for their future endeavors. The CAREER award also provided ample opportunities for my research group and me to forge into new research directions given the broad scope of the proposed work. Ultimately, this freedom has led to a number of new and exciting results regarding the nature of deformation in Earth's crust, Earth's response to moderate sized earthquakes occurring hundreds of kilometers away, and further new software development to handle these new, massive, datasets provided by the EarthScope program. The culmination of these efforts allowed me a much smoother path toward tenure, given that the CAREER grant enabled new directions and production through integration of my teaching and research (as well as my national service to the EarthScope program). The challenges to this integration were quite modest given that I was able to fold my group's research directly into some of my teaching. Finally, while the program is very good at present, I will present a few ideas for program improvement. For example, it is essential that NSF continue to fully inform and educate peer reviewers of the special nature of CAREER awards, since it is a major challenge for most reviewers to fully and adequately judge both research and teaching. Further, because of the unique nature of the CAREER proposal, NSF might consider extending the length of the proposal by 2-3 pages to provide additional room for extended project timelines, etc.

Preliminary Results of P & S-wave Teleseismic Tomography of the Superior Region

NASA Astrophysics Data System (ADS)

Bollmann, T. A.; van der Lee, S.; Frederiksen, A. W.

2013-12-01

In continental North America, the Midcontinent Rift System (MRS) is the most prominent feature in gravity and magnetic anomaly maps. These anomalies are associated with large amount of igneous material deposited there around 1.1 Ga. Preliminary evidence from ambient seismic noise analysis of the area has found that the MRS crustal structure has a low velocity along its axis. A major question remains as to whether any structural evidence for the MRS' rifting episodes or its failure were retained in the lithospheric mantle beneath it. To this end we measured teleseismic P and S travel times at Earthscope seismic stations from the Flexible Array SPREE, the Transportable Array, and several US ANSS Backbone stations. These measurements constitute a major resource for upgrading an existing teleseismic, pre-SPREE tomography model for the region, (Frederiksen et al., 2013) as well as longer wavelength regional models, such as NA07 (Bedle and Van der Lee, 2007). We measured the delay times of about 25 thousand teleseismic P arrivals from over a hundred events with magnitudes of 5.5 and greater, and about half as many for S arrivals. Nearly half of these teleseismic events are to the NNW (Alaska-Japan) and about one third are from Central and South America to the SSE. We inverted the P delays for common station-side delays and common event-side delays. Station-side P delays vary by about 1.5 s over the region, with the Archean Superior Craton recording earlier arrivals than Proterozoic terrains in Wisconsin. SPREE stations show later arrivals closer to the rift axis compare to earlier onesfurther away from the rift, but a correlation with the large rift-related gravity anomaly is not obvious. To examine whether the mantle has any rift-related structures, for example from meltdepletion, we are measuring delay times from additional events recorded and recovered during the spring SPREE service run, applying corrections to the delay times for topography and crustal structure, and will invert the corrected delay times for 3D mantle structure. The average P-wave delay time from all events for each station fit to a surface. An interpolated surface of these values is shown in the background. The gray lines are accretionary provinces from Whitmeyer & Karlstrom (2007).

Local Upper Mantle Upwelling beneath New England: Evidence from Seismic Anisotropy.

NASA Astrophysics Data System (ADS)

Levin, V. L.; Long, M. D.; Lopez, I.; Li, Y.; Skryzalin, P. A.

2017-12-01

The upper mantle beneath eastern North America contains regions where seismic wave speed is significantly reduced. As they cut across the trend of the Appalachian terranes, these anomalies likely post-date the Paleozoic assembly of Pangea. Most prominent of them, the North Appalachian Anomaly (NAA), has been alternatively explained by the localized disruption of lithospheric fabric, the passage of the Great Meteor Hot Spot, and the current local upwelling of the asthenosphere. Comprehensive mapping of shear wave splitting identified a local perturbation of an otherwise uniform regional pattern, with no apparent splitting occurring at a site within the NAA. To evaluate the reality of this apparent localized disruption in the anisotropic fabric of the upper mantle beneath northeastern North America we used observations of shear wave splitting from a set of long-running observatories not included in previous studies. Three methods of evaluating shear wave splitting (rotation-correlation, minimization of the transverse component, and the splitting intensity) yield complementary results. We show that splitting of core-refracted shear waves within the outline of the NAA is significantly weaker than towards its edges and beyond them (Figure 1). Average fast orientations are close to the absolute plate motion in the hot-spot reference frame, thus we can attribute a large fraction of this signal to the coherently sheared sub-lithospheric upper mantle. A decrease in average delay we observe, from 1 s outside the NAA to under 0.2 s within it, translates into a reduction of the vertical extent of the sheared layer from 130 km to 16 km (assuming 4% anisotropy), or alternatively into a weakening of the azimuthal anisotropy from 5% to 0.6% (assuming a 100 km thick layer). The splitting reduction within the NAA is consistent with a localized change in anisotropic fabric that would be expected in case of geologically recent sub-vertical flow overprinting the broadly uniform upper mantle fabric detected throughout the region. Figure 1. Splitting intensity (red circles) plotted over best-fitting sinusoidal functions (blue, parameters in upper right) and predictions based on average delays and fast polarizations (green, parameters in upper left). Outlines of the NAA at 200 km depth from tomographic studies using Earthscope data.

A Broadband Investigation of the Texas/Gulf of Mexico Passive Margin

NASA Astrophysics Data System (ADS)

Evanzia, D.; Ainsworth, R.; Pratt, K. W.; Pulliam, J.; Gurrola, H.

2012-12-01

The lithosphere of central and east Texas underwent two cycles of continental rifting and orogeny from the formation of Laurentia and assembly through the breakup of Pangea. The craton itself, exposed in the Llano uplift of central Texas, formed ~1.4 Ga as part of the great expanse of Mesoproterozoic crust that makes up southern Laurentia. Some of this crust was deformed during the Grenville orogeny ~1.1 Ga. Southern Laurentia was subsequently stable until rifting began in Cambrian time (~530 Ma). Suturing of Gondwana to Laurentia (310-290 Ma) during the assembly of Pangea formed the Ouachita orogen in west Texas. Sometime before 200 Ma rifting was initiated, opening the Gulf of Mexico (GoM). In north and east Texas the Ouachita front lies north of GoM rifting but, according to deep seismic data, Ouachita structures appear to coincide with GoM rifting in south and central Texas. This suggests that rifting in that region occurred along structures that were weakened previously by Ouachita deformation and reactivated during the Jurassic opening of the GoM. It is not clear whether the process that created the Gulf of Mexico and led to the formation of Texas' Gulf Coast Plain (GCP) is best described as "active" or "passive" rifting. A recent study interpreted the GCP to be a volcanic rifted margin—an active rifting process—using available gravity, magnetic, drilling and geological data, but older studies describe the opening of the GoM as a passive event. In the coastal plain, a large magnetic anomaly suggests that the crust here was modified by volcanism. Seismic data are sparse and of limited quality in the Gulf Coast region so we conducted a 2.5-year broadband seismograph transect across the GCP in an effort to clarify its structure and origin. In all, twenty-three broadband seismographs were deployed in a line from Matagorda Island, in the Gulf of Mexico, to Johnson City, TX, on the uplifted Llano Plateau from July 2010 to December 2012. These seismographs have an average spacing of 15 km and coincided with the deployment of EarthScope Transportable Array stations in central and east Texas. We will present the results of P- and S-wave tomographic inversions for upper mantle structure beneath the array.

Geodetic Constraints on Fault Slip Rates and Seismic Hazard in the Greater Las Vegas Area

NASA Astrophysics Data System (ADS)

Hammond, W. C.; Kreemer, C.; Blewitt, G.; Broermann, J.; Bennett, R. A.

2014-12-01

We address fundamental questions about how contemporary tectonic deformation of the crust in the southern Great Basin occurs in the region around Las Vegas (LV) Nevada, western Arizona and eastern California. This area lies in the intersection of the eastern Walker Lane Belt, southern Great Basin and western Colorado Plateau (CP), sharing features of transtensional and extensional deformation associated with Pacific/North America relative motion. We use GPS data collected from 48 stations of the MAGNET semi-continuous network and 77 stations from continuous networks including BARGEN and EarthScope Plate Boundary Observatory. MAGNET stations have been observed for a minimum of 7 years, while most continuous stations have longer records. From these data we estimate the velocity of crustal motion for all stations with respect to the stable North America reference frame NA12. To correct for transients from recent large earthquakes including the 1999 Hector Mine and 2010 El Mayor-Cucapah events we use models of co- and post-seismic deformation, subtracting the predicted motions from the time series before estimating interseismic stain rates. We find approximately 2 mm/yr of relative motion distributed over 200 km centered on Las Vegas, with a mean strain accumulation rate of 10 × 10-9 yr-1, with lower rates of predominantly extensional strain to the east and higher rates of predominantly shear deformation to the west. The mean strain rate is lower than that of the western Walker Lane but about twice that of eastern Nevada where e.g., the Wells, NV MW 6.0 earthquake occurred in 2008. From this new velocity field we generated a horizontal tensor strain rate map and a crustal block motion model to portray the transition of active strain from the CP into the Walker Lane. For faults in the Las Vegas Valley, including the Eglington Fault and Frenchman Mountain Fault, the observed velocity gradients and model results are consistent with normal slip rates of 0.2 mm/yr, which are typical for the region. The Stateline Fault system experiences dextral slip of at least 0.4 mm/yr while normal faults south of LV collectively accommodate 0.9 mm/yr of east-west extension across a zone ~150 km wide. We see no evidence for concentrations of deformation or isolated rigid microplates within this zone.

Constructing a starting 3D shear velocity model with sharp interfaces for SEM-based upper mantle tomography in North America

NASA Astrophysics Data System (ADS)

Calo, M.; Bodin, T.; Yuan, H.; Romanowicz, B. A.; Larmat, C. S.; Maceira, M.

2013-12-01

Seismic tomography is currently evolving towards 3D earth models that satisfy full seismic waveforms at increasingly high frequencies. This evolution is possible thanks to the advent of powerful numerical methods such as the Spectral Element Method (SEM) that allow accurate computation of the seismic wavefield in complex media, and the drastic increase of computational resources. However, the production of such models requires handling complex misfit functions with more than one local minimum. Standard linearized inversion methods (such as gradient methods) have two main drawbacks: 1) they produce solution models highly dependent on the starting model; 2) they do not provide a means of estimating true model uncertainties. However, these issues can be addressed with stochastic methods that can sample the space of possible solutions efficiently. Such methods are prohibitively challenging computationally in 3D, but increasingly accessible in 1D. In previous work (Yuan and Romanowicz, 2010; Yuan et al., 2011) we developed a continental scale anisotropic upper mantle model of north America based on a combination of long period seismic waveforms and SKS splitting measurements, showing the pervasive presence of layering of anisotropy in the cratonic lithosphere with significant variations in depth of the mid-lithospheric boundary. The radial anisotropy part of the model has been recently updated using the spectral element method for forward wavefield computations and waveform data from the latest deployments of USarray (Yuan and Romanowicz, 2013). However, the long period waveforms (periods > 40s) themselves only provide a relatively smooth view of the mantle if the starting model is smooth, and the mantle discontinuities necessary for geodynamical interpretation are not imaged. Increasing the frequency of the computations to constrain smaller scale features is possible, but challenging computationally, and at the risk of falling in local minima of the misfit function. In this work we propose instead to directly tackle the non-linearity of the inverse problem by using stochastic methods to construct a 3D starting model with a good estimate of the depths of the main layering interfaces. We present preliminary results of the construction of such a starting 3D model based on: (1) Regionalizing the study area to define provinces within which lateral variations are smooth; (2) Applying trans-dimensional stochastic inversion (Bodin et al., 2012) to obtain accurate 1D models in each province as well as the corresponding error distribution, constrained by receiver function and surface wave dispersion data as well as the previously constructed 3D model (name), and (3) connecting these models laterally using data-driven smoothing operators to obtain a starting 3D model with errors. References Bodin, T.,et al. 2012, Transdimensional inversion of receiver functions and surface wave dispersion, J. Geophys. Res., 117, B02301, doi:10.1029/2011JB008560. Yuan and Romanowicz, 2013, in revison. Yuan, H., et al. 2011, 3-D shear wave radially and azimuthally anisotropic velocity model of the North American upper mantle. Geophysical Journal International, 184: 1237-1260. doi: 10.1111/j.1365-246X.2010.04901.x Yuan, H. & Romanowicz, B., 2010. Lithospheric layering in the North American Craton, Nature, 466, 1063-1068.

Crustal structure beneath the Blue Mountains terranes and cratonic North America, eastern Oregon, and Idaho, from teleseismic receiver functions

NASA Astrophysics Data System (ADS)

Christian Stanciu, A.; Russo, Raymond M.; Mocanu, Victor I.; Bremner, Paul M.; Hongsresawat, Sutatcha; Torpey, Megan E.; VanDecar, John C.; Foster, David A.; Hole, John A.

2016-07-01

We present new images of lithospheric structure obtained from P-to-S conversions defined by receiver functions at the 85 broadband seismic stations of the EarthScope IDaho-ORegon experiment. We resolve the crustal thickness beneath the Blue Mountains province and the former western margin of cratonic North America, the geometry of the western Idaho shear zone (WISZ), and the boundary between the Grouse Creek and Farmington provinces. We calculated P-to-S receiver functions using the iterative time domain deconvolution method, and we used the H-k grid search method and common conversion point stacking to image the lithospheric structure. Moho depths beneath the Blue Mountains terranes range from 24 to 34 km, whereas the crust is 32-40 km thick beneath the Idaho batholith and the regions of extended crust of east-central Idaho. The Blue Mountains group Olds Ferry terrane is characterized by the thinnest crust in the study area, 24 km thick. There is a clear break in the continuity of the Moho across the WISZ, with depths increasing from 28 km west of the shear zone to 36 km just east of its surface expression. The presence of a strong midcrustal converting interface at 18 km depth beneath the Idaho batholith extending 20 km east of the WISZ indicates tectonic wedging in this region. A north striking 7 km offset in Moho depth, thinning to the east, is present beneath the Lost River Range and Pahsimeroi Valley; we identify this sharp offset as the boundary that juxtaposes the Archean Grouse Creek block with the Paleoproterozoic Farmington zone.

Shallow and deep creep events observed and quantified with strainmeters along the San Andreas Fault near Parkfield

NASA Astrophysics Data System (ADS)

Mencin, D.; Hodgkinson, K. M.; Mattioli, G. S.; Johnson, W.; Gottlieb, M. H.; Meertens, C. M.

2016-12-01

Three-component strainmeter data from numerous borehole strainmeters (BSM) along the San Andreas Fault (SAF), including those that were installed and maintained as part of the EarthScope Plate Boundary Observatory (PBO), demonstrate that the characteristics of creep propagation events with sub-cm slip amplitudes can be quantified for slip events at 10 km source-to-sensor distances. The strainmeters are installed at depths of approximately 100 - 250 m and record data at a rate of 100 samples per second. Noise levels at periods of less than a few minutes are 10-11 strain, and for periods in the bandwidth hours to weeks, the periods of interest in the search for slow slip events, are of the order of 10-8 to 10-10 strain. Strainmeters, creepmeters, and tiltmeters have been operated along the San Andreas Fault, observing creep events for decades. BSM data proximal to the SAF cover a significant temporal portion of the inferred earthquake cycle along this portion of the fault. A single instrument is capable of providing broad scale constraints of creep event asperity size, location, and depth and moreover can capture slow slip, coseismic rupture as well as afterslip. The synthesis of these BSM data presents a unique opportunity to constrain the partitioning between aseismic and seismic slip on the central SAF. We show that the creepmeters confirm that creep events that are imaged by the strainmeters, previously catalogued by the authors, are indeed occurring on the SAF, and are simultaneously being recorded on local creepmeters. We further show that simple models allow us to loosely constrain the location and depth of the creep event on the fault, even with a single instrument, and to image the accumulation and behavior of surface as well as crustal creep with time.

Magmatic arc structure around Mount Rainier, WA, from the joint inversion of receiver functions and surface wave dispersion

NASA Astrophysics Data System (ADS)

Obrebski, Mathias; Abers, Geoffrey A.; Foster, Anna

2015-01-01

The deep magmatic processes in volcanic arcs are often poorly understood. We analyze the shear wave velocity (VS) distribution in the crust and uppermost mantle below Mount Rainier, in the Cascades arc, resolving the main velocity contrasts based on converted phases within P coda via source normalization or receiver function (RF) analysis. To alleviate the trade-off between depth and velocity, we use long period phase velocities (25-100 s) obtained from earthquake surface waves, and at shorter period (7-21 s) we use seismic noise cross correlograms. We use a transdimensional Bayesian scheme to explore the model space (VS in each layer, number of interfaces and their respective depths, level of noise on data). We apply this tool to 15 broadband stations from permanent and Earthscope temporary stations. Most results fall into two groups with distinctive properties. Stations east of the arc (Group I) have comparatively slower middle-to-lower crust (VS = 3.4-3.8 km/s at 25 km depth), a sharp Moho and faster uppermost mantle (VS = 4.2-4.4 km/s). Stations in the arc (Group II) have a faster lower crust (VS = 3.7-4 km/s) overlying a slower uppermost mantle (VS = 4.0-4.3 km/s), yielding a weak Moho. Lower crustal velocities east of the arc (Group I) most likely represent ancient subduction mélanges mapped nearby. The lower crust for Group II ranges from intermediate to felsic. We propose that intermediate-felsic to felsic rocks represent the prearc basement, while intermediate composition indicates the mushy andesitic crustal magmatic system plus solidified intrusion along the volcanic conduits. We interpret the slow upper mantle as partial melt.

Relating the Seismic Character of the Crust and Upper Mantle to Late-Cenozoic Extension in Southwestern N.A.

NASA Astrophysics Data System (ADS)

Thurner, S.; Frassetto, A.; Porter, R.; Zandt, G.

2008-12-01

A recent tectonic reconstruction (McQuarrie and Wernicke, 2005) places detailed constraints on the magnitude and scope of late-Cenozoic extension throughout Southwestern North America. This project seeks to better understand the distribution of extension throughout the crust and upper mantle and elucidate the transition from the highly extended Basin and Range to the relatively unextended Colorado Plateau. To this end, we present teleseismic receiver functions generated from 31 broadband seismometers associated with EarthScope's BigFoot Array, TriNet, and PASSCAL stations deployed across Southern California and Arizona. We employ the common-conversion-point stacking method to analyze variations in lithospheric structure. Additionally, in regions with clear converted wave reverberations we analyze the trade-off between crustal thickness and bulk Vp/Vs to improve our view of how crustal thickness and Vp/Vs relate to different tectonic environments and degree of extension. Our preliminary estimates indicate crustal thicknesses of ~25-30 km in eastern California increasing to ~40- 45 km within the southern Colorado Plateau. The transition between thin to thick crust appears to occur over as little as 20 km. Crustal Vp/Vs varies considerably, with Vp/Vs greater than 1.8 near the Transverse Ranges and Colorado Plateau, and less than 1.8 in the southern Basin and Range. We also view a change in the nature of the Moho approaching the Colorado Plateau. Initial calculations indicate the amplitude of the converted wave from the Moho is twice as strong beneath the Mojave and Southern Basin and Range than the Colorado Plateau. Additionally, we observe laminated crust in the western Mojave Desert approaching the Transverse Ranges.

Delay Times From Clustered Multi-Channel Cross Correlation and Simulated Annealing

NASA Astrophysics Data System (ADS)

Creager, K. C.; Sambridge, M. S.

2004-12-01

Several techniques exist to estimate relative delay times of seismic phases based on the assumption that the waveforms observed at several stations can be expressed as a common waveform that has been time shifted and distorted by random uncorrelated noise. We explore the more general problem of estimating the relative delay times for regional or even global distributions of seismometers in cases where waveforms vary systematically across the array. The estimation of relative delay times is formulated as a global optimization of the weighted sum of squares of cross correlations of each seismogram pair evaluated at the corresponding difference in their relative delay times. As there are many local minima in this penalty function, a simulated annealing algorithm is used to obtain a solution. The weights depend strongly on the separation distance among seismogram pairs as well as a measure of the similarity of waveforms. Thus, seismograph pairs that are physically close to each other and have similar waveforms are expected to be well aligned while those with dissimilar waveforms or large separation distances are severely down-weighted and thus need not be well aligned. As a result noisy seismograms, which are not similar to other seismograms, are down-weighted so they do not adversely effect the relative delay times of other seismograms. Finally, natural clusters of seismograms are determined from the weight matrix. Examples of aligning a few hundred P and PKP waveforms from a broadband global array and from a mixed broadband and short-period continental-scale array will be shown. While this method has applications in many situations, it may be especially useful for arrays such as the EarthScope Bigfoot Array.

Moho Structure of the Central Sierra Nevada From an EarthScope Flex Array Deployment

NASA Astrophysics Data System (ADS)

Burdick, S.; Zandt, G.; Gilbert, H.; Jones, C.; Owens, T.

2005-12-01

Findings from the southern Sierra Nevada (south of 37 degrees north) show that the crustal thickness in the southern Sierra Nevada range does not obey an Airy isostasy model. Receiver function data show that the crustal thickness generally increases across the range from the high eastern peaks to the low western foothills, and the Moho discontinuity disappears beneath parts of the western foothills. This disappearance of the Moho has been attributed to the entrainment of the crust into the mantle by the convective removal of the southern batholithic root during the past 3-4 M yrs (Zandt et al., Nature, 2004). Other possible causes of Moho disappearance include a very gradational, or even inverted, impedance contrast due to lower crustal or upper mantle wavespeed anomalies. During the summer of 2005, the Sierra Nevada Earthscope Project (SNEP) has deployed an Earthscope flex array of over forty broadband seismometers with 25 km spacing, designed to constrain lithospheric structure of the central Sierra Nevada between the latitudes of approximately 37 to 38 degrees north. We will report on a receiver function study to better define the boundaries of the Moho "hole" to the north. Initial receiver functions from the first stations deployed mainly on the western and eastern flanks of the range show a northward continuation of both the "hole" under the western margin and a high amplitude Moho under the eastern flank of the range. This new observation suggests either the Moho disappearance is unrelated to the convective removal of the southern root or that root removal has affected the Sierra Nevada significantly farther north than suggested by presently available volcanic and xenolith evidence. Receiver functions collected from SNEP data will be processed into move-out corrected depth stacks in order to present a more complete map of Moho depth and amplitude beneath the region. To quantify the range of impedance contrasts capable of producing the observed variability in Moho amplitude, observed receiver function arrivals will be compared to synthetic examples calculated for a range of lower crustal and upper mantle wavespeeds. In conjunction with other studies these results should lead to a better understanding of the scale and processes associated with a young lithospheric foundering event.

The Plate Boundary Observatory: Current status and plans for the next five years

NASA Astrophysics Data System (ADS)

Mattioli, G. S.; Feaux, K.; Meertens, C. M.; Mencin, D.; Miller, M.

2013-12-01

UNAVCO currently operates and maintains the NSF-funded Plate Boundary Observatory (PBO), which is the geodetic facility of EarthScope. PBO was designed and built from 2003 to 2008 with $100M investment from the NSF Major Research Equipment and Facilities Construction (MREFC) Program. UNAVCO operated and maintained PBO under a Cooperative Agreement (CA) with NSF from 2008 to 2013 and will continue PBO O&M for the next five years as part of the new Geodesy Advancing Geosciences and EarthScope (GAGE) Facility. PBO is largest continuous GPS and borehole geophysical network in the Americas, with 1100 continuous Global Positioning System (cGPS) sites, including several with multiple monuments, 79 boreholes, with 75 tensor strainmeters, 78 short-period, 3-component seismometers, and pore pressure sensors at 23 sites. PBO also includes 26 tiltmeters deployed at volcanoes in Alaska, Mt St Helens, and Yellowstone caldera and 6 long-baseline laser strainmeters. Surface meteorological sensors are collocated at 154 GPS sites. UNAVCO provides high-rate (1 Hz), low-latency (<1 s) GPS data streams (RT-GPS) from 382 stations in PBO. UNAVCO has delivered over 62 Tb of geodetic data to the EarthScope community since its PBO's inception in 2004. Over the past year, data return for the cGPS component of PBO is 98%, well above the data return metric of 85% set by the NSF, a result of efforts to upgrade power systems and communications infrastructure. In addition, PBO has set the standard for the design, construction, and operation of other multi-hazard networks across the Americas, including COCONet in the Caribbean region and TLALOCNet in Mexico. Funding to support ongoing PBO O&M has declined from FY2012 CA levels under the new GAGE Facility. The implications for data return and data quality metrics as well as replacement of aging PBO GPS instruments with GNSS-compatible systems are as yet unknown. A process to assess the cost of specific PBO components, data rates, enhanced capabilities, and method of delivery (i.e. continuous streams vs. archived files) relative to their scientific value will be proposed. In addition, options to partner with other federal mission-oriented agencies and possible commercial ventures also will be discussed. 1100 station PBO continuous GPS Network.

Arc Crustal Structure around Mount Rainier Constrained by Receiver Functions and Seismic Noise

NASA Astrophysics Data System (ADS)

Obrebski, M. J.; Abers, G. A.; Foster, A. E.

2013-12-01

Volcanic arcs along subduction zones are thought to be loci for continental growth. Nevertheless, the amount of material transferred from the mantle to crust and the associated magmatic plumbing are poorly understood. While partial melting of mantle peridotite produces basaltic melt, the average composition of continental crust is andesitic. Several models of magma production, migration and differentiation have been proposed to explain the average crust composition in volcanic arcs. The formation of mafic cumulate and restite during fractional crystallization and partial melting has potential to alter the structure of the crust-mantle interface (Moho). The computed composition and distribution of crust and mantle rocks based on these different models convert into distinctive vertical velocity profiles, which seismic imaging methods can unravel . With a view to put more constraints on magmatic processes in volcanic arc, we analyze the shear wave velocity (Vs) distribution in the crust and uppermost mantle below Mount Rainier, WA, in the Cascadia arc. We resolve the depth of the main velocity contrasts based on converted phases, for which detection in the P coda is facilitated by source normalization or receiver function (RF) analysis. To alleviate the trade-off between depth and velocity intrinsic to RF analysis, we jointly invert RF with frequency-dependent surface wave velocities. We analyze earthquake surface waves to constrain long period dispersion curves (20-100 s). For shorter period (5-20s), we use seismic noise cross-correlograms and Aki's spectral formulation, which allows longer periods for given path. We use a transdimensional Bayesian scheme to explore the model space (shear velocity in each layer, number of interfaces and their respective depths). This approach tends to minimize the number of layers required to fit the observations given their noise level. We apply this tool to a set of broad-band stations from permanent and EarthScope temporary stations, all within 35 km of Mt Rainier. The receiver functions significantly differ from one station to another, indicating short wavelength lateral contrast in the lithospheric structure. Below arc stations offset from Mount Rainier, preliminary models show a rather clear Moho transition around 40km, separating lower crust with 3.6-3.9 km/s shear velocity, from a ~ 20 km thick mantle lid with Vs ~ 4.2 km/s. In contrast, at station PANH located 9 km east of Mount Rainier, the exact location of the Moho is not clear. Shear velocity ranges from 3.3 to 3.9 km/s from the surface down to 55 km depth, with the exception of a fast layer imaged between 25 and 32 km depth with Vs ~ 4.2 km/s. It seems likely that partial melt in the mantle, combined with high-velocity underplated or differentiated lower crust, are acting in various ways to create a complicated structure around the Moho.

Crustal Structure beneath Alaska from Receiver Functions

NASA Astrophysics Data System (ADS)

Zhang, Y.; Li, A.

2017-12-01

The crustal structure in Alaska has not been well resolved due to the remote nature of much of the state. The USArray Transportable Array (TA), which is operating in Alaska and northwestern Canada, significantly increases the coverage of broadband seismic stations in the region and allows for a more comprehensive study of the crust. We have analyzed P-receiver functions from earthquake data recorded by 76 stations of the TA and AK networks. Both common conversion point (CCP) and H-K methods are used to estimate the mean crustal thickness. The results from the CCP stacking method show that the Denali fault marks a sharp transition from thick crust in the south to thin crust in the north. The thickest crust up to 52 km is located in the St. Elias Range, which has been formed by oblique collision between the Yakutat microplate and North America. A thick crust of 48 km is also observed beneath the eastern Alaska Range. These observations suggest that high topography in Alaska is largely compensated by the thick crust root. The Moho depth ranges from 28 km to 35 km beneath the northern lowlands and increases to 40-45 km under the Books Range. The preliminary crustal thickness from the H-K method generally agrees with that from the CCP stacking with thicker crust beneath high mountain ranges and thinner crust beneath lowlands and basins. However, the offshore part is not well constrained due to the limited coverage of stations. The mean Vp/Vs ratio is around 1.7 in the Yukon-Tanana terrane and central-northern Alaska. The ratio is about 1.9 in central and southern Alaska with higher values at the Alaska Range, Wrangell Mountains, and St. Elias Range. Further data analyses are needed for obtaining more details of the crustal structure in Alaska to decipher the origin and development of different tectonic terranes.

ADVANCED WAVEFORM SIMULATION FOR SEISMIC MONITORING EVENTS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Helmberger, Donald V.; Tromp, Jeroen; Rodgers, Arthur J.

The recent Nevada Earthquake (M=6) produced an extraordinary set of crustal guided waves. In this study, we examine the three-component data at all the USArray stations in terms of how well existing models perform in predicting the various phases, Rayleigh waves, Love waves, and Pnl waves. To establish the source parameters, we applied the Cut and Paste Code up to distance of 5° for an average local crustal model which produced a normal mechanism (strike=35°,dip=41°,rake=-85°) at a depth of 9 km and Mw=5.9. Assuming this mechanism, we generated synthetics at all distances for a number of 1D and 3D models.more » The Pnl observations fit the synthetics for the simple models well both in timing (VPn=7.9km/s) and waveform fits out to a distance of about 5°. Beyond this distance a great deal of complexity can be seen to the northwest apparently caused by shallow subducted slab material. These paths require considerable crustal thinning and higher P-velocities. Small delays and advances outline the various tectonic province to the south, Colorado Plateau, etc. with velocities compatible with that reported on by Song et al.(1996). Five-second Rayleigh waves (Airy Phase) can be observed throughout the whole array and show a great deal of variation ( up to 30s). In general, the Love waves are better behaved than the Rayleigh waves. We are presently adding higher frequency to the source description by including source complexity. Preliminary inversions suggest rupture to northeast with a shallow asperity. We are, also, inverting the aftershocks to extend the frequencies to 2 Hz and beyond following the calibration method outlined in Tan and Helmberger (2007). This will allow accurate directivity measurements for events with magnitude larger than 3.5. Thus, we will address the energy decay with distance as s function of frequency band for the various source types.« less

Lg Attenuation Anisotropy Across the Western US

NASA Astrophysics Data System (ADS)

Phillips, W. S.; Rowe, C. A.; Stead, R. J.; Begnaud, M. L.

2017-12-01

The USArray has allowed us to map seismic attenuation of local and regional phases to unprecedented spatial extent and resolution. Following standard mantle Pn velocity anisotropy methods, we have incorporated azimuthal anisotropy into our tomographic inversion of high-frequency Lg amplitudes. The Lg is a crustal shear phase made up of many trapped modes, thus results can be considered to be crustal averages. Azimuthal anisotropy reduces residual variance by just over 10% for 1.5-3 Hz Lg. We observe a median anisotropic variation of 12%, and a high of 50% in the Salton Trough. Low attenuation (high-Q) directions run parallel to topographic fabric and major strike slip faults in tectonically active areas, and often run parallel to mantle shear wave splitting directions in stable regions. Tradeoffs are of concern, and synthetic tests show that elongated attenuation anomalies will produce anisotropy artifacts, but of factors 2-3 times lower than observations. In particular, the strength of a long, narrow high-Q anomaly will trade off with high-Q directions parallel to the long axis, while an elongated low-Q anomaly will trade off with high-Q directions perpendicular to the long axis. We observe an elongated low-Q anomaly associated with the Walker Lane; however, observed high-Q directions run parallel to the long axis of this anomaly, opposite to the tradeoff effect, supporting the anisotropic observation, and implying that the effect may be underestimated. Further, we observe an elongated high-Q anomaly associated with the Great Valley and Sierra Nevada that runs across the long axis, again opposite to the tradeoff effect. This study was performed using waveforms, event locations and phase picks made available by IRIS, NEIC and ANF, and processing was done using semi-automated means, thus this is a technique that can be applied quickly to study crustal anisotropy over large areas when appropriate station density is available.

Crustal Structure and Subsidence of the Williston Basin: Evidence from Receiver Function Stacking and Gravity Modeling

NASA Astrophysics Data System (ADS)

Song, J.; Liu, K. H.; Yu, Y.; Mickus, K. L.; Gao, S. S.

2017-12-01

The Williston Basin of the northcentral United States and southern Canada is a typical intracratonic sag basin, with nearly continuous subsidence from the Cambrian to the Jurassic. A number of contrasting models on the subsidence mechanism of this approximately circular basin have been proposed. While in principle 3D variations of crustal thickness, layering, and Poisson's ratio can provide essential constraints on the models, thick layers of Phanerozoic sediment with up to 4.5 km thickness prevented reliable determinations of those crustal properties using active or passive source seismic techniques. Specifically, the strong reverberations of teleseismic P-to-S converted waves (a.k.a. receiver functions or RFs) from the Moho and intracrustal interfaces in the loose sedimentary layer can severely contaminate the RFs. Here we use RFs recorded by about 200 USArray and other stations in the Williston Basin and adjacent areas to obtain spatial distributions of the crustal properties. We have found that virtually all of the RFs recorded by stations in the Basin contain strong reverberations, which are effectively removed using a recently developed deconvolution-based filter (Yu et al., 2015, DOI: 10.1002/2014JB011610). A "double Moho" structure is clearly imaged beneath the Basin. The top interface has a depth of about 40 km beneath the Basin, and shallows gradually toward the east from the depocenter. It joins with the Moho beneath the western margin of the Superior Craton, where the crust is about 30 km thick. The bottom interface has a depth of 55 km beneath the Wyoming Craton, and deepens to about 70 km beneath the depocenter. Based on preliminary results of H-k stacking and gravity modeling, we interpret the layer between the two interfaces as a high density, probably eclogized layer. Continuous eclogitization from the Cambrian to the Jurassic resulted in the previously observed rates of subsidence being nearly linear rather than exponential.

Mitigating artifacts in back-projection source imaging with implications for frequency-dependent properties of the Tohoku-Oki earthquake

NASA Astrophysics Data System (ADS)

Meng, Lingsen; Ampuero, Jean-Paul; Luo, Yingdi; Wu, Wenbo; Ni, Sidao

2012-12-01

Comparing teleseismic array back-projection source images of the 2011 Tohoku-Oki earthquake with results from static and kinematic finite source inversions has revealed little overlap between the regions of high- and low-frequency slip. Motivated by this interesting observation, back-projection studies extended to intermediate frequencies, down to about 0.1 Hz, have suggested that a progressive transition of rupture properties as a function of frequency is observable. Here, by adapting the concept of array response function to non-stationary signals, we demonstrate that the "swimming artifact", a systematic drift resulting from signal non-stationarity, induces significant bias on beamforming back-projection at low frequencies. We introduce a "reference window strategy" into the multitaper-MUSIC back-projection technique and significantly mitigate the "swimming artifact" at high frequencies (1 s to 4 s). At lower frequencies, this modification yields notable, but significantly smaller, artifacts than time-domain stacking. We perform extensive synthetic tests that include a 3D regional velocity model for Japan. We analyze the recordings of the Tohoku-Oki earthquake at the USArray and at the European array at periods from 1 s to 16 s. The migration of the source location as a function of period, regardless of the back-projection methods, has characteristics that are consistent with the expected effect of the "swimming artifact". In particular, the apparent up-dip migration as a function of frequency obtained with the USArray can be explained by the "swimming artifact". This indicates that the most substantial frequency-dependence of the Tohoku-Oki earthquake source occurs at periods longer than 16 s. Thus, low-frequency back-projection needs to be further tested and validated in order to contribute to the characterization of frequency-dependent rupture properties.

A Three - Dimensional Receiver Function Study of the Western United States

NASA Astrophysics Data System (ADS)

Lindsey, C.; Gurrola, H.

2008-12-01

The western United States has a complex geologic history and has been the focus of many regional scale PASSCAL seismic studies that investigate depth variations to the Moho, the 410 km discontinuity, and the 660 km discontinuities. Analysis of depth variations to the Moho in relation to topography is important in understanding the isostatic compensation depth, the thermal state of the upper mantle and boundaries between tectonic provinces. Analysis of the 410 and 660 km discontinuities allow us to determine variations in mantle temperature at these depths and facilitates comparison with tectonic boundaries. This abstract summarizes results from stacking Pds phases throughout the western US using data from all available previous PASSCAL studies in the western U.S. together with data from the EarthScope Transportable array. These data sets enable us to produce an image over the entire western US from the Pacific coast to the Rocky mountain front. Common conversion point stacking of Pds phases was performed by back projecting the data through a 3-D seismic velocity model (surface wave tomography model NA04 by Van der Lee). The images produced show large variations in Moho topography with an average depth of 39.6 kilometer over the western US with ± 7.2 km standard deviation in depth. As would be expected the Moho appears to be deepest beneath the Colorado Plateau and central Montana and shallowest throughout the Basin and Raange. The Moho also appears very shallow beneath eastern Washington. There is a band oof thick crust along the Yellowstone hot spot track. The 410 km discontinuity appears to have a mean depth of 427 km with a standard deviation in depth of ± 10.2 km. At this time the images are still very noisy but in a regional sense the 410 appears deepest beneath the southern part of the image and shallower to the north. Depths to the 660 km discontinuity appear to average 675 km with standard deviation of ± 9.8 km. The 660 does not appear to have a north-south change in depth but appears deepest to the Eastern part of the image and shallower to the west. This relationship may indicate that the thermal state of the 410 is controlled by high temperatures to the south associated with the Basin and Range and cooler to the north were subduction is present. The 660 may be controlled by the transition from warm oceanic and transitional lithosphere to the west and cooler continental lithosphere to the east.

Background Lamb waves in the Earth's atmosphere

NASA Astrophysics Data System (ADS)

Nishida, Kiwamu; Kobayashi, Naoki; Fukao, Yoshio

2014-01-01

Lamb waves of the Earth's atmosphere in the millihertz band have been considered as transient phenomena excited only by large events. Here, we show the first evidence of background Lamb waves in the Earth's atmosphere from 0.2 to 10 mHz, based on the array analysis of microbarometer data from the USArray in 2012. The observations suggest that the probable excitation source is atmospheric turbulence in the troposphere. Theoretically, their energy in the troposphere tunnels into the thermosphere at a resonant frequency via thermospheric gravity wave, where the observed amplitudes indeed take a local minimum. The energy leak through the frequency window could partly contribute to thermospheric wave activity.

Making it and breaking it in the Midwest: Continental assembly and rifting from modeling of EarthScope magnetotelluric data

USGS Publications Warehouse

Bedrosian, Paul A.

2016-01-01

A three-dimensional lithospheric-scale resistivity model of the North American mid-continent has been estimated based upon EarthScope magnetotelluric data. Details of the resistivity model are discussed in relation to lithospheric sutures, defined primarily from aeromagnetic and geochronologic data, which record the southward growth of the Laurentian margin in the Proterozoic. The resistivity signature of the 1.1 Ga Mid-continent Rift System is examined in detail, in particular as relates to rift geometry, extent, and segmentation. An unrecognized expanse of (concealed) Proterozoic deltaic deposits in Kansas is identified and speculated to result from axial drainage along the southwest rift arm akin to the Rio Grande delta which drains multiple rift basins. A prominent conductor traces out Cambrian rifting in Arkansas, Missouri, Tennessee, and Kentucky; this linear conductor has not been imaged before and suggests that the Cambrian rift system may have been more extensive than previously thought. The highest conductivity within the mid-continent is imaged in Minnesota, Michigan, and Wisconsin where it is coincident with Paleoproterozoic metasedimentary rocks. The high conductivity is attributed to metallic sulfides, and in some cases, graphite. The former is a potential source of sulfur for multiple mineral deposits types, occurrences of which are found throughout the region. Finally, the imprint left within the mantle following the 1.1 Ga rifting event is examined. Variations in lithospheric mantle conductivity are observed and are interpreted to reflect variations in water content (depleted versus metasomatized mantle) imprinted upon the mantle by the Keweenawan mantle plume.

UNAVCO GPS High-Rate and Real-Time Products and Services: Building a next generation geodetic network.

NASA Astrophysics Data System (ADS)

Mencin, David; Meertens, Charles; Mattioli, Glen; Feaux, Karl; Looney, Sara; Sievers, Charles; Austin, Ken

2013-04-01

Recent advances in GPS technology and data processing are providing position estimates with centimeter-level precision at high-rate (1-5 Hz) and low latency (<1 s). Broad community interest in these data is growing rapidly because these data will have the potential to improve our understanding in diverse areas of geophysics including properties of seismic, volcanic, magmatic and tsunami deformation sources, and moreover profoundly transforming rapid event characterization, early warning, as well as hazard mitigation and response. Other scientific and operational applications for high-rate GPS also include glacier and ice sheet motions, tropospheric modeling, and better constraints on the dynamics of space weather. UNAVCO, through community input and the recent Plate Boundary Observatory (PBO) NSF-ARRA Cascadia initiative, has nearly completed the process of upgrading a total of 373 PBO GPS sites to real-time high-rate capability and these streams are now being archived in the UNAVCO data center. Further, through the UNAVCO core proposal (GAGE), currently under review at NSF, UNAVCO has proposed upgrading a significant portion of the ~1100 GPS stations that PBO currently operates to real-time high-rate capability to address community science and operational needs. In addition, in collaboration with NOAA, 74 of these stations will provide meteorological data in real-time, primarily to support watershed and flood analyses for regional early-warning systems related to NOAA's work with California Department of Water Resources. In preparation for this increased emphasis on high-rate GPS data, UNAVCO hosted an NSF funded workshop in Boulder, CO on March 26-28, 2012, which brought together 70 participants representing a spectrum of research fields with a goal to develop a community plan for the use of real-time GPS data products within the UNAVCO and EarthScope communities. These data products are expected to improve and expand the use of real-time, high-rate GPS data over the next decade.

UNAVCO Geodetic HIgh-Rate and Real-Time Products and Services: A next generation geodetic network

NASA Astrophysics Data System (ADS)

Mattioli, G. S.; Mencin, D.; Meertens, C. M.; Feaux, K.; Looney, S.

2012-12-01

Recent advances in GPS technology and data processing are providing position estimates with centimeter-level precision at high-rate (1 Hz) and low latency (<1 s). These data will have the potential to improve our understanding in diverse areas of geophysics including properties of seismic, volcanic, magmatic and tsunami deformation sources, and moreover profoundly transforming rapid event characterization, early warning, as well as hazard mitigation and response. Other scientific and operational applications for high-rate GPS also include glacier and ice sheet motions, tropospheric modeling, and better constraints on the dynamics of space weather. UNAVCO, through community input and the recent Plate Boundary Observatory (PBO) NSF-ARRA Cascadia initiative, has nearly completed the process of upgrading a total of 373 PBO GPS sites to real-time high-rate capability and these streams are now being archived in our data center. In addition, UNAVCO hosted an NSF funded workshop in Boulder, CO on March 26-28, which brought together 70 participants representing a spectrum of research fields with a goal to develop a community plan for the use of real-time GPS data products within the UNAVCO and EarthScope communities. These data products are expected to improve and expand the use of real-time GPS data over the next decade. Additionally, in collaboration with NOAA, 74 of these stations will provide meteorological data in real-time, primarily to support watershed and flood analyses for regional early-warning systems related to NOAA's work with California Department of Water Resources. As part of this upgrade UNAVCO is also exploring making the 75 PBO borehole strainmeter sites, whose data are now collected with a latency of 24 hours, available in SEED format in real-time in the near future, providing an opportunity to combine high-rate surface positioning and strain data together.

New constraints on slip rates and locking depths of the San Andreas Fault System from Sentinel-1A InSAR and GAGE GPS observations

NASA Astrophysics Data System (ADS)

Ward, L. A.; Smith-Konter, B. R.; Higa, J. T.; Xu, X.; Tong, X.; Sandwell, D. T.

2017-12-01

After over a decade of operation, the EarthScope (GAGE) Facility has now accumulated a wealth of GPS and InSAR data, that when successfully integrated, make it possible to image the entire San Andreas Fault System (SAFS) with unprecedented spatial coverage and resolution. Resulting surface velocity and deformation time series products provide critical boundary conditions needed for improving our understanding of how faults are loaded across a broad range of temporal and spatial scales. Moreover, our understanding of how earthquake cycle deformation is influenced by fault zone strength and crust/mantle rheology is still developing. To further study these processes, we construct a new 4D earthquake cycle model of the SAFS representing the time-dependent 3D velocity field associated with interseismic strain accumulation, co-seismic slip, and postseismic viscoelastic relaxation. This high-resolution California statewide model, spanning the Cerro Prieto fault to the south to the Maacama fault to the north, is constructed on a 500 m spaced grid and comprises variable slip and locking depths along 42 major fault segments. Secular deep slip is prescribed from the base of the locked zone to the base of the elastic plate while episodic shallow slip is prescribed from the historical earthquake record and geologic recurrence intervals. Locking depths and slip rates for all 42 fault segments are constrained by the newest GAGE Facility geodetic observations; 3169 horizontal GPS velocity measurements, combined with over 53,000 line-of-sight (LOS) InSAR velocity observations from Sentinel-1A, are used in a weighted least-squares inversion. To assess slip rate and locking depth sensitivity of a heterogeneous rheology model, we also implement variations in crustal rigidity throughout the plate boundary, assuming a coarse representation of shear modulus variability ranging from 20-40 GPa throughout the (low rigidity) Salton Trough and Basin and Range and the (high rigidity) Central Valley and ocean lithosphere.

Investigation of the lithosphere of the Texas Gulf Coast using phase-specific Ps receiver functions produced by wavefield iterative deconvolution

NASA Astrophysics Data System (ADS)

Gurrola, H.; Berdine, A.; Pulliam, J.

2017-12-01

Interference between Ps phases and reverberations (PPs, PSs phases and reverberations thereof) make it difficult to use Ps receiver functions (RF) in regions with thick sediments. Crustal reverberations typically interfere with Ps phases from the lithosphere-asthenosphere boundary (LAB). We have developed a method to separate Ps phases from reverberations by deconvolution of all the data recorded at a seismic station by removing phases from a single wavefront at each iteration of the deconvolution (wavefield iterative deconvolution or WID). We applied WID to data collected in the Gulf Coast and Llano Front regions of Texas by the EarthScope Transportable array and by a temporary deployment of 23 broadband seismometers (deployed by Texas Tech and Baylor Universities). The 23 station temporary deployment was 300 km long; crossing from Matagorda Island onto the Llano uplift. 3-D imaging using these data shows that the deepest part of the sedimentary basin may be inboard of the coastline. The Moho beneath the Gulf Coast plain does not appear in many of the images. This could be due to interference from reverberations from shallower layers or it may indicate the lack of a strong velocity contrast at the Moho perhaps due to serpentinization of the uppermost mantle. The Moho appears to be flat, at 40 km) beneath most of the Llano uplift but may thicken to the south and thin beneath the Coastal plain. After application of WID, we were able to identify a negatively polarized Ps phase consistent with LAB depths identified in Sp RF images. The LAB appears to be 80-100 km deep beneath most of the coast but is 100 to 120 km deep beneath the Llano uplift. There are other negatively polarized phases between 160 and 200 km depths beneath the Gulf Coast and the Llano Uplift. These deeper phases may indicate that, in this region, the LAB is transitional in nature and rather than a discrete boundary.

Promoting seismology education and research via the IRIS Education and Public Outreach Program

NASA Astrophysics Data System (ADS)

Taber, J. J.; Bravo, T. K.; Dorr, P. M.; Hubenthal, M.; Johnson, J. A.; McQuillan, P.; Sumy, D. F.; Welti, R.

2015-12-01

The Incorporated Research Institutions for Seismology's Education and Public Outreach (EPO) program is committed to advancing awareness and understanding of seismology and geophysics, while inspiring careers in the Earth sciences. To achieve this mission, IRIS EPO combines content and research expertise of consortium membership with educational and outreach expertise of IRIS staff to create a portfolio of programs, products, and services that target a range of audiences, including grades 6-12 students and teachers, undergraduate and graduate students, faculty, and the general public. IRIS also partners with UNAVCO and other organizations in support of EarthScope where the facilities are well-suited for sustained engagement of multiple audiences. Examples of research-related EPO products and services include the following resources. Tools developed in collaboration with IRIS Data Services provide public and educational access to data, and to a suite of data products. Teachers can stream seismic data from educational or research sensors into their classroom, and the Active Earth Monitor display, designed for visitor centers, universities and small museums, provides views of recent data along with animations that explain seismology concepts, and stories about recent research. Teachable Moment slide sets, created in collaboration with the University of Portland within 24 hours of major earthquakes, provide interpreted USGS tectonic maps and summaries, animations, visualizations, and other event-specific information so educators can explore newsworthy earthquakes with their students. Intro undergraduate classroom activities have been designed to introduce students to some grand challenges in seismological research, while our Research Experiences for Undergraduates program pairs students with seismology researchers throughout the Consortium and provides the opportunity for the students to present their research at a national meeting. EPO activities are evaluated via a combination of internal and external assessments, with an emphasis on formative evaluation and regular review by an advisory committee of community members. Results from our assessments inform the program's decision-making process, which has allowed IRIS to significantly enhance its EPO activities over time.

PBO Integrated Real-Time Observing Sites at Volcanic Sites

NASA Astrophysics Data System (ADS)

Mencin, D.; Jackson, M.; Borsa, A.; Feaux, K.; Smith, S.

2009-05-01

The Plate Boundary Observatory, an element of NSF's EarthScope program, has six integrated observatories in Yellowstone and four on Mt St Helens. These observatories consist of some combination of borehole strainmeters, borehole seismometers, GPS, tiltmeters, pore pressure, thermal measurements and meteorological data. Data from all these instruments have highly variable data rates and formats, all synchronized to GPS time which can cause significant congestion of precious communication resources. PBO has been experimenting with integrating these data streams to both maximize efficiency and minimize latency through the use of software that combines the streams, like Antelope, and VPN technologies.

Cyberinfrastructure for Online Access to High-Quality Data: Advances and Opportunities (Invited)

NASA Astrophysics Data System (ADS)

Baru, C.

2010-12-01

Advanced cyberinfrastructure capabilities are enabling end-to-end management of data flows in observing system networks and online access to very large data archives. We provide an overview of several projects in earth and environmental sciences that have developed and deployed cyberinfrastructure for collecting and organizing field observations and remote sensing data, to make them available to a community of users. The data cyberinfrastructure framework should cover the range from data acquisition, quality control, data archiving, discovery, access, integration, and modeling. Using examples from different earth and environmental science cyberinfrastructure efforts, we will describe the state of the art in data cyberinfrastructure and future directions and challenges. The Tropical Ecology, Assessment and Monitoring (TEAM) Network (http://teamnetwork.org), which is a network of forested sites—currently consisting of 15 sites, and growing—distributed across Central America, South America, Africa, and Asia. Each site implements a standardized set of data collection protocols, all under the control of a common cyberinfrastructure. The data are available via a portal from a central site, but with appropriate access controls. The TEAM Network is run by Conservation International, in partnership with the Wildlife Conservation Society, Smithsonian Institute, and the Missouri Botanical Gardens, and is funded by the Moore Foundation. The EarthScope Data Portal (portal.earthscope.org) implements a virtual metadata catalog and a data cart to provides a means for simultaneously exploring EarthScope's various instrument networks, as well as seamlessly downloading data from multiple stations and instrument types. The prototype of the US Geoinformatics Information Network (US GIN) project is implementing a federated catalog, using the Catalog Services for Web (CSW) standard. The NSF-funded Opentopography.org—a spinoff of the GEON project, www.geongrid.org—provides online access to curated topography data and associated software tools and services. A related effort, funded by the NASA ROSES program, hosts high-altitude and satellite-based LiDAR data. We will highlight data cyberinfrastructure capabilities and issues related to these efforts. Given the rapidly increasing volumes of data, the data cyberinfrastructure must be scalable to very large dataset sizes, large numbers of data sets, and a large user community. New computing capabilities are emerging to tackle this data deluge, from very large memory systems to highly parallel platforms. The next NSF supercomputer, called Gordon, will provide 64TB of solid-state memory and over 220TB of solid-state disk. NSF has also made available a shared-nothing Hadoop cluster with 700 processors for testing cloud computing strategies. We will discuss a number of opportunities and challenges in exploiting such systems for data intensive scientific computing.

Velocity and Density Models Incorporating the Cascadia Subduction Zone for 3D Earthquake Ground Motion Simulations

USGS Publications Warehouse

Stephenson, William J.

2007-01-01

In support of earthquake hazards and ground motion studies in the Pacific Northwest, three-dimensional P- and S-wave velocity (3D Vp and Vs) and density (3D rho) models incorporating the Cascadia subduction zone have been developed for the region encompassed from about 40.2°N to 50°N latitude, and from about -122°W to -129°W longitude. The model volume includes elevations from 0 km to 60 km (elevation is opposite of depth in model coordinates). Stephenson and Frankel (2003) presented preliminary ground motion simulations valid up to 0.1 Hz using an earlier version of these models. The version of the model volume described here includes more structural and geophysical detail, particularly in the Puget Lowland as required for scenario earthquake simulations in the development of the Seattle Urban Hazards Maps (Frankel and others, 2007). Olsen and others (in press) used the model volume discussed here to perform a Cascadia simulation up to 0.5 Hz using a Sumatra-Andaman Islands rupture history. As research from the EarthScope Program (http://www.earthscope.org) is published, a wealth of important detail can be added to these model volumes, particularly to depths of the upper-mantle. However, at the time of development for this model version, no EarthScope-specific results were incorporated. This report is intended to be a reference for colleagues and associates who have used or are planning to use this preliminary model in their research. To this end, it is intended that these models will be considered a beginning template for a community velocity model of the Cascadia region as more data and results become available.

Report on the Aseismic Slip, Tremor, and Earthquakes Workshop

USGS Publications Warehouse

Gomberg, Joan; Roeloffs, Evelyn; Trehu, Anne; Dragert, Herb; Meertens, Charles

2008-01-01

This report summarizes the discussions and information presented during the workshop on Aseismic Slip, Tremor, and Earthquakes. Workshop goals included improving coordination among those involved in conducting research related to these phenomena, assessing the implications for earthquake hazard assessment, and identifying ways to capitalize on the education and outreach opportunities presented by these phenomena. Research activities of focus included making, disseminating, and analyzing relevant measurements; the relationships among tremor, aseismic or 'slow-slip', and earthquakes; and discovering the underlying causative physical processes. More than 52 participants contributed to the workshop, held February 25-28, 2008 in Sidney, British Columbia. The workshop was sponsored by the U.S. Geological Survey, the National Science Foundation?s Earthscope Program and UNAVCO Consortium, and the Geological Survey of Canada. This report has five parts. In the first part, we integrate the information exchanged at the workshop as it relates to advancing our understanding of earthquake generation and hazard. In the second part, we summarize the ideas and concerns discussed in workshop working groups on Opportunities for Education and Outreach, Data and Instrumentation, User and Public Needs, and Research Coordination. The third part presents summaries of the oral presentations. The oral presentations are grouped as they were at the workshop in the categories of phenomenology, underlying physical processes, and implications for earthquake hazards. The fourth part contains the meeting program and the fifth part lists the workshop participants. References noted in parentheses refer to the authors of presentations made at the workshop, and published references are noted in square brackets and listed in the Reference section. Appendix A contains abstracts of all participant presentations and posters, which also have been posted online, along with presentations and author contact information at http://www.earthscope.org/science/cascadia.

Drought-induced uplift in the western United States as observed by the EarthScope Plate Boundary Observatory GPS network

NASA Astrophysics Data System (ADS)

Borsa, A. A.; Agnew, D. C.; Cayan, D. R.

2014-12-01

The western United States (WUS) has been experiencing severe drought since 2013. The solid earth response to the accompanying loss of surface and near-surface water mass should be a broad region of uplift. We use seasonally-adjusted time series from continuously operating GPS stations in the EarthScope Plate Boundary Observatory and several smaller networks to measure this uplift, which reaches 15 mm in the California Coastal Ranges and Sierra Nevada and has a median value of 4 mm over the entire WUS. The pattern of mass loss due to the drought, which we recover from an inversion of uplift observations, ranges up to 50 cm of water equivalent and is consistent with observed decreases in precipitation and streamflow. We estimate the total deficit to be 240 Gt, equivalent to a uniform 10 cm layer of water over the entire region, or the magnitude of the current annual mass loss from the Greenland Ice Sheet. In the WUS, interannual changes in crustal loading are driven by changes in cool-season precipitation, which cause variations in surface water, snowpack, soil moisture, and groundwater. The results here demonstrate that the existing network of continuous GPS stations can be used to recover loading changes due to both wet and dry climate patterns. This suggests a new role for GPS networks such as that of the Plate Boundary Observatory. The exceptional stability of the GPS monumentation means that this network is also capable of monitoring the long-term effects of regional climate change. Surface displacement observations from GPS have the potential to expand the capabilities of the current hydrological observing network for monitoring current and future hydrological changes, with obvious social and economic benefits.

Support of EarthScope GPS Campaigns at the UNAVCO Facility

NASA Astrophysics Data System (ADS)

Boyce, E.; Blume, F.; Normandeau, J.

2008-12-01

In order to support portable GPS deployments funded by the NSF's EarthScope Science panel, PBO has purchased 100 campaign GPS systems. Based Topcon GB-1000 equipment, the systems have been designed for stand-alone temporary or semi-permanent deployment that will be used for densifying areas not sufficiently covered by continuous GPS, and responding to volcanic and tectonic crises. UNAVCO provides support for all aspects of these projects, including proposal and budget development, project planning, equipment design, field support, and data archiving. Ten of the 100 systems have been equipped with real-time kinematic (RTK) capability requiring additional radio and data logging equipment. RTK systems can be used to rapidly map fault traces and profile fault escarpments and collect precise position information for GIS based geologic mapping. Each portable self-contained campaign systems include 18 Ah batteries, a regulated 32 watt solar charging system, and a low-power dual frequency GPS receiver and antenna in a waterproof case with security enhancements. The receivers have redundant memory sufficient for storing over a year's worth of data as well as IP and serial communications capabilities for longer-term deployments. Monumentation options are determined on a project-by-project basis, with options including Tech2000 masts, low-profile spike mounts, and traditional tripods and optical tribrachs. Drilled-braced monuments or masts can be installed for "semi- permanent" style occupations. The systems have been used to support several projects to date, including the University of Washington's 30-unit deployment to monitor the Episodic Tremor and Slip event in November, 2005 and the ongoing Rio Grande Rift experiment, run by the Universities of Colorado, Utah State, and New Mexico, which has seen the construction of 25 permanent monuments in 2006 and 2007 and a 26-site campaign reoccupation in 2008.

Support of EarthScope GPS Campaigns at the UNAVCO Facility

NASA Astrophysics Data System (ADS)

Boyce, E.; Blume, F.; Normandeau, J.

2007-12-01

In order to support portable GPS deployments funded by the NSF's EarthScope Science panel, PBO has purchased 100 campaign GPS systems. Based Topcon GB-1000 equipment, the systems have been designed for stand-alone temporary or semi-permanent deployment that will be used for densifying areas not sufficiently covered by continuous GPS, and responding to volcanic and tectonic crises. UNAVCO provides support for all aspects of these projects, including proposal and budget development, project planning, equipment design, field support, and data archiving. Ten of the 100 systems will be purchased with real-time kinematic (RTK) capability requiring additional radio and data logging equipment. RTK systems can be used to rapidly map fault traces and profile fault escarpments and collect precise position information for GIS based geologic mapping. Each portable self-contained campaign systems include 18 Ah batteries, a regulated 32 watt solar charging system, and a low-power dual frequency GPS receiver and antenna in a waterproof case with security enhancements. The receivers have redundant memory sufficient for storing over a year's worth of data as well as IP and serial communications capabilities for longer-term deployments. Monumentation options are determined on a project-by-project basis, with options including Tech2000 masts, low-profile spike mounts, and traditional tripods and optical tribrachs. Drilled-braced monuments or masts can be installed for "semi-permanent" style occupations. The systems have been used to support several projects to date, including the University of Washington's 30- unit deployment to monitor the Episodic Tremor and Slip event in November, 2005 and the ongoing Rio Grande Rift experiment, run by the Universities of Colorado, Utah State, and New Mexico, which has seen the construction of 25 permanent monuments in 2006 and 2007.

Overview of the Ocean Bottom Seismology Component of the Cascadia Initiative (Invited)

NASA Astrophysics Data System (ADS)

Toomey, D. R.; Allen, R. M.; Collins, J. A.; Dziak, R. P.; Hooft, E. E.; Livelybrooks, D.; McGuire, J. J.; Schwartz, S. Y.; Tolstoy, M.; Trehu, A. M.; Wilcock, W. S.

2013-12-01

We report on the experimental progress of the ocean bottom seismology component of the Cascadia Initiative (CI). The CI is an onshore/offshore seismic and geodetic experiment that takes advantage of an Amphibious Array Facility (AAF) to study questions ranging from megathrust earthquakes to volcanic arc structure to the formation, deformation and hydration of the Juan de Fuca and Gorda plates. This diverse set of objectives are all components of understanding the overall subduction zone system and require an array that provides high quality data that crosses the shoreline and encompasses relevant plate boundaries. In October 2010, an open community workshop was convened in Portland, Oregon that produced a series of recommendations to maximize the scientific return of the CI and to develop deployment plans for the offshore component of the experiment. The NSF Cascadia Initiative Workshop Report1 presents the scientific objectives of the CI, the resources involved and the community-defined ocean bottom seismometer (OBS) deployment plan. There are several noteworthy aspects of the CI: The CI is the first to utilize a new generation of OBSs that are designed to withstand trawling by fisheries, thus allowing the collection of seismic data in the shallow water that overlies much of the Cascadia megathrust. The CI is a plate-scale experiment that provides a unique opportunity to study the structure and dynamics of an entire oceanic plate, from its birth at a spreading center to its subduction beneath a continental plate. Together with the land stations that are part of the amphibious array and other land networks, the OBSs will provide coverage at a density comparable to the Transportable Array of Earthscope from the volcanic arc out to the Pacific-Juan de Fuca spreading center segments. The CI is a community experiment that provides open access to all data via the IRIS Data Management Center, thus ensuring that the scientific return from the investment of resources is maximized. Lastly, the CI includes a significant education and outreach component that is providing berths for students, post-docs and other scientists to participate in either deployment or recovery legs, thus providing the seismological community with opportunities to gain valuable experience in planning and carrying out an OBS experiment. The Cascadia Initiative Expedition Team (CIET) is a group of scientists who are leading the seagoing expeditions to deploy and recover OBSs and are developing related Education and Outreach modules. The CIET maintains a web site for the community where information regarding CI expeditions and OBS metadata are provided2. The CI is currently in its third year of data acquisition. The CIET presentation will report on the 2011-2013 field seasons, data quantity and quality, ongoing E&O efforts, and the schedule for OBS operations in 2014.

U-Pb thermochronology of the lower crust: producing a long-term record of craton thermal evolution

NASA Astrophysics Data System (ADS)

Blackburn, T.; Bowring, S. A.; Mahan, K. H.; Perron, T.; Schoene, B.; Dudas, F. O.

2010-12-01

The EarthScope initiative is focused on providing an enhanced view of the North American lithosphere and the present day stress field of the North American continent. Of key interest is the interaction between convecting asthenosphere and the conducting lithospheric mantle that underlie the continents, especially the cold ‘keels’ that underlie Archean domains. Cratonic regions are in general characterized by minimal erosion and or sediment accumulation. The Integration of seismic tomography, and mantle xenolith studies reveal a keel of seismically fast and relatively buoyant and viscous mantle; physical properties that are intimately linked with the long-term stability and topographic expression of the region. Missing from this model of the continental lithosphere is the 4th dimension--time--and along with it our understanding of the long-term evolution of these stable continental interiors. Here we present a thermal record from the North American craton using U-Pb thermochronology of lower crustal xenoliths. The use of temperature sensitive dates on lower crustal samples can produce a unique time-temperature record for a well-insulated and slowly cooling lithosphere. The base of the crust is insulated enough to remain unperturbed by any plausible changes to surface topography, yet unlike the subadjacent lithospheric mantle, contains accessory phases amenable to U-Pb dating (rutile, apatite, titanite). With near steady state temperatures in the lower crust between 400-600 °C, U-Pb thermochronometers with similar average closure temperatures for Pb are perfectly suited to record the long-term cooling of the lithosphere. Xenoliths from multiple depths, and across the craton yield time-temperature paths produced from U-Pb thermochronometers that record extremely slow cooling (<0.25 °C/Ma) over time scales of billions of years. Combining these data with numerical thermal modeling allow constraints to be placed on the dominant heat transfer mechanisms operating within the lithosphere including exhumation, conduction, decay of heat producing elements and thickness of crustal layers/lithospheric mantle. The thermal histories produced from this numerical model can in turn be used to calculate model U-Pb thermochronometric data using a numerical solution to the diffusion/production equation. Integration of thermal and volume diffusion models for the U-Pb system suggests that the extreme slow cooling recorded by U-Pb thermochronology is consistent with low integrated exhumation rates (<0.005 km/Ma). This exhumation rate is integrated over time-scales of hundreds of million to a billion years and does not preclude the possibility for rapid or short-wave length uplift/subsidence. This long-term record of continental lithosphere stability and apparent neutral buoyancy of the craton within a cooling mantle may be further used to refine our estimates of secular cooling within the mantle.

Tomotectonic constraints on deformation of Cordilleran North America since Late Jurassic

NASA Astrophysics Data System (ADS)

Mihalynuk, M. G.; Sigloch, K.

2017-12-01

Seismic tomography reveals detailed mantle structure beneath North America, largely thanks to USArray. TWO massive composite slabs are recognized down to 2000 km depth and their topologies are combined with quantitative plate reconstructions back to the breakup of Pangea using Atlantic and Pacific magnetic isochrons. This tomotectonic analysis reveals evolving arc/trench-plate geometries of a vast archipelago/microcontinent and ocean plateau that were overridden by North America, and an explanation for Cordilleran deformation episodes. As Pangea fragmented, subduction reconfigured from EAST-directed beneath the continent (during final growth of the Intermontane Superterrane, IMS, or "AltaBC"), to WEST-directed beneath an intraoceanic, massive arc chevron (MAC). MAC trenches were stationary within a mantle reference frame, as indicated by near-vertical slab walls 4-7x as thick as mature ocean lithosphere, and its trenches were >10,000 km long. East-pointing MAC apex was located 2000-4000 km off Pangea's west coast where MAC arc was built atop the Insular superterrane (INS, or "BajaBC"), a microcontinent extending >2600 km southwards from the apex. Ocean lithosphere between the MAC apex and west-drifting North America was consumed by 155 Ma. INS, comparable in length to the Indian subcontinent, initially collided with the leading edge of North America/IMS and generated "Nevadan" deformation. Diachronous Sevier deformation followed as MAC was driven farther into the continental margin and raked southward (sinistral offsets w.r.t. North America). By 130 Ma, with large segments accreted and MAC geometry breaking down, subduction was forced to jump outboard (westward) of MAC. The Franciscan accretionary complex marks a return to eastward/Andean-style subduction (of the Farallon plate). A remarkably complete analogue for collision at 130 Ma is found in modern Australia's override of arcs to its north. Rapid northward transport of BajaBC w.r.t. North America 90-50 Ma is attributed to arrival of the buoyant Shatsky conjugate plateau on the Farallon plate 90 Ma, which coupled with BajaBC lithosphere, as recorded by slab truncation, paleomagnetic measurements, an extinguished Sierra Nevada arc (80 Ma), subducted sediments underplated far inboard of the margin, and Laramide deformation.

Fine Scale Structure of Low and Ultra-Low Velocity Patches in the Lowermost Mantle: Some Case Studies

NASA Astrophysics Data System (ADS)

Yuan, K.; Romanowicz, B. A.; French, S.

2015-12-01

The lowermost part of the mantle, which is roughly halfway to the center of the earth, plays a key role as a thermal and chemical boundary layer between the solid, silicate mantle and fluid, iron outer core. Constraining the seismic velocity structure in this region provides important insights on mantle dynamics, and core-mantle interactions. Recently, global shear wave velocity tomography has confirmed the presence of broad plume conduits extending vertically through the lower mantle in the vicinity of major hotspots (SEMUCB-WM1, French and Romanowicz, 2015). These conduits are rooted in D" in patches of strongly reduced shear velocity, at least some of which, such as Hawaii, appear to contain known ultra low velocity zones (e.g. Cottaar and Romanowicz, 2012). We seek to determine whether these patches generally contain ULVZs, and to contrast them with less extreme structures such as the PERM anomaly (Lekic et al., 2012). Because global tomography cannot resolve such fine scale structure, we apply forward modeling of higher frequency (10-20s) Sdiff waveforms in 3D complex structures using the Spectral Element Method. We focus on Iceland, Hawaii and the PERM anomaly, and Sdiff observations at USArray and/or dense broadband arrays in Europe. In all three cases, Sdiff waveforms are clearly distorted by these anomalies, with either a complex coda and/or evidence for amplitude focusing. As a start, we design simple cylindrical models of shear velocity reduction, and contrast the best fitting ones at each location considered in terms of diameter, height above the core-mantle boundary and strength of velocity reduction. We refine previously obtained models for Hawaii and the Perm Anomaly. For Iceland, the waveforms show a strong azimuthally dependent post-cursor, with maximum travel time delay of ~20s and focusing effects. The preliminary best fitting model shows a structure of 700km in diameter, ~15% reduction in shear wave velocity, extending ~40 km above the core-mantle boundary, in a location close to the Iceland hotspot which is in agreement with the low velocity patch in model SEMUCB_WM1.

Adapting Controlled-source Coherence Analysis to Dense Array Data in Earthquake Seismology

NASA Astrophysics Data System (ADS)

Schwarz, B.; Sigloch, K.; Nissen-Meyer, T.

2017-12-01

Exploration seismology deals with highly coherent wave fields generated by repeatable controlled sources and recorded by dense receiver arrays, whose geometry is tailored to back-scattered energy normally neglected in earthquake seismology. Owing to these favorable conditions, stacking and coherence analysis are routinely employed to suppress incoherent noise and regularize the data, thereby strongly contributing to the success of subsequent processing steps, including migration for the imaging of back-scattering interfaces or waveform tomography for the inversion of velocity structure. Attempts have been made to utilize wave field coherence on the length scales of passive-source seismology, e.g. for the imaging of transition-zone discontinuities or the core-mantle-boundary using reflected precursors. Results are however often deteriorated due to the sparse station coverage and interference of faint back-scattered with transmitted phases. USArray sampled wave fields generated by earthquake sources at an unprecedented density and similar array deployments are ongoing or planned in Alaska, the Alps and Canada. This makes the local coherence of earthquake data an increasingly valuable resource to exploit.Building on the experience in controlled-source surveys, we aim to extend the well-established concept of beam-forming to the richer toolbox that is nowadays used in seismic exploration. We suggest adapted strategies for local data coherence analysis, where summation is performed with operators that extract the local slope and curvature of wave fronts emerging at the receiver array. Besides estimating wave front properties, we demonstrate that the inherent data summation can also be used to generate virtual station responses at intermediate locations where no actual deployment was performed. Owing to the fact that stacking acts as a directional filter, interfering coherent wave fields can be efficiently separated from each other by means of coherent subtraction. We propose to construct exploration-type trace gathers, systematically investigate the potential to improve the quality and regularity of realistic synthetic earthquake data and present attempts at separating transmitted and back-scattered wave fields for the improved imaging of Earth's large-scale discontinuities.

Working with strainmeter data

USGS Publications Warehouse

Hodgkinson, Kathleen M.; Agnew, Duncan; Roeloffs, Evelyn A.

2013-01-01

The Plate Boundary Observatory (PBO), the geodetic component of the U.S. National Science Foundation–funded Earthscope program, includes 75 borehole and 6 laser strainmeters (http://pbo.unavco.org). The strainmeters are installed at several locations: on the Cascadia forearc in Washington state and on Vancouver Island, Canada; in arrays of two to nine instruments along the North American–Pacific plate boundary in California; at Mount St. Helens; and in Yellowstone National Park. For deformation signals seconds to weeks in duration, strainmeters have a resolution and a signal-to-noise ratio superior to those of seismometers and GPS. However, this high sensitivity can introduce nontectonic signals into strain data, presenting data interpretation challenges, especially for borehole strainmeters.

TLALOCNet continuous GPS-Met Array in Mexico supporting the 2017 NAM GPS Hydrometeorological Network.

NASA Astrophysics Data System (ADS)

Cabral-Cano, E.; Salazar-Tlaczani, L.; Adams, D. K.; Vivoni, E. R.; Grutter, M.; Serra, Y. L.; DeMets, C.; Galetzka, J.; Feaux, K.; Mattioli, G. S.; Miller, M. M.

2017-12-01

TLALOCNet is a network of continuous GPS and meteorology stations in Mexico to study atmospheric and solid earth processes. This recently completed network spans most of Mexico with a strong coverage emphasis on southern and western Mexico. This network, funded by NSF, CONACyT and UNAM, recently built 40 cGPS-Met sites to EarthScope Plate Boundary Observatory standards and upgraded 25 additional GPS stations. TLALOCNet provides open and freely available raw GPS data, and high frequency surface meteorology measurements, and time series of daily positions. This is accomplished through the development of the TLALOCNet data center (http://tlalocnet.udg.mx) that serves as a collection and distribution point. This data center is based on UNAVCO's Dataworks-GSAC software and also works as part of UNAVCO's seamless archive for discovery, sharing, and access to GPS data. The TLALOCNet data center also contains contributed data from several regional GPS networks in Mexico for a total of 100+ stations. By using the same protocols and structure as the UNAVCO and other COCONet regional data centers, the scientific community has the capability of accessing data from the largest Mexican GPS network. This archive provides a fully queryable and scriptable GPS and Meteorological data retrieval point. In addition, real-time 1Hz streams from selected TLALOCNet stations are available in BINEX, RTCM 2.3 and RTCM 3.1 formats via the Networked Transport of RTCM via Internet Protocol (NTRIP) for real-time seismic and weather forecasting applications. TLALOCNet served as a GPS-Met backbone for the binational Mexico-US North American Monsoon GPS Hydrometeorological Network 2017 campaign experiment. This innovative experiment attempts to address water vapor source regions and land-surface water vapor flux contributions to precipitation (i.e., moisture recycling) during the 2017 North American Monsoon in Baja California, Sonora, Chihuahua, and Arizona. Models suggest that moisture recycling is a large contributor to summer rainfall. This experiment represents a first attempt to quantify the surface water vapor flux contribution to GPS-derived precipitable water vapor. Preliminary results from this campaign are presented.

Seismological Constraints on Lithospheric Evolution in the Appalachian Orogen

NASA Astrophysics Data System (ADS)

Fischer, K. M.; Hopper, E.; Hawman, R. B.; Wagner, L. S.

2017-12-01

Crust and mantle structures beneath the Appalachian orogen, recently resolved by seismic data from the EarthScope SESAME Flexible Array and Transportable Array, provide new constraints on the scale and style of the Appalachian collision and subsequent lithospheric evolution. In the southern Appalachians, imaging with Sp and Ps phases reveals the final (Alleghanian) suture between the crusts of Laurentia and the Gondwanan Suwannee terrane as a low angle (<15°) southward-dipping interface that soles into a flat-lying mid-crustal detachment. The suture location near the top of the crust coincides closely with the northern limit of the Suwannee terrane reconstructed from its lower Paleozoic shelf strata (Boote and Knapp, 2016). The observed suture geometry implies over 300 km of head-on shortening across a plate boundary structure similar in scale to the Himalayan mid-crustal detachment. While the suture and other structures from the Alleghanian collision are preserved in the upper and mid-crust, the lower crust and mantle lithosphere beneath this region have been significantly modified by later processes. Ps receiver functions, wavefield migration and SsPmp modeling reveal that crustal thickness reaches a maximum of 58 km (beneath high elevations in the Blue Ridge terrane) and decreases to 29-35 km (beneath lower elevations in the Carolina and Suwannee terranes). Given metamorphic estimates of unroofing (Duff and Kellogg, 2017) isostatic arguments indicate crustal thicknesses were 15-25 km larger at the end of the orogeny, indicating a thick crustal root across the region. The present-day residual crustal root beneath the Blue Ridge mountains is estimated to have a density contrast with the mantle of only 104±20 kg/m3. This value is comparable to other old orogens but lower than values typical of young or active orogens, indicating a loss of lower crustal buoyancy over time. At mantle depths, the negative shear velocity gradient that marks the transition from lithosphere to asthenosphere, as illuminated by Sp phases, varies across the Appalachian orogen. This boundary is shallow beneath the northeastern U.S. and in the zone of Eocene volcanism in Virginia, where low velocity anomalies occur in the upper mantle. These correlations suggest recent active lithosphere-asthenosphere interaction.

Building and Modification of the Continental Lithosphere: the History of the Contiguous U.S. as told by MLDs and LABs

NASA Astrophysics Data System (ADS)

Hopper, E.; Fischer, K. M.

2016-12-01

The lithosphere preserves a record of past and present tectonic processes in its internal structures and its boundary with the underlying asthenosphere. We use common conversion point stacked Sp converted waves recorded by EarthScope's Transportable Array, as well as other available permanent and temporary broadband stations, to image such structures in the lithospheric mantle of the contiguous U.S. In the tectonically youngest western U.S., a shallow, sharp velocity gradient at the base of the lithosphere suggests a boundary defined by ponded melt. The lithosphere thickens with age of volcanism, implying the lithosphere is a melt-mitigated, conductively cooling thermal boundary layer. Beneath older, colder lithosphere where melt fractions are likely much lower, the velocity gradient at the base of such a layer should be a more diffuse, primarily thermal boundary. This is consistent with observations in the eastern U.S. where the lithosphere-asthenosphere boundary (LAB) is locally sharp and shallower only in areas of inferred enhanced upwelling - such as ancient hot spot tracks and areas of inferred delamination. In the cratonic interior, the LAB is even more gradual in depth, and is transparent to Sp waves with dominant periods of 10 s. Although seismic imaging only provides a snapshot of the lithosphere as it is today, preserved internal structures extend the utility of this imaging back into deep geological time. Ancient accretion within the cratonic lithospheric mantle is preserved as dipping structures associated with relict subducted slabs from Paleoproterozoic continental accretion, suggesting that lateral accretion was integral to the cratonic mantle root formation process. Metasomatism, melt migration and ponding below a carbonated peridotite solidus explain a sub-horizontal mid-lithospheric discontinuity (MLD) commonly observed at 70-100 km depth. This type of MLD is strongest in Mesoproterozoic and older lithosphere, suggesting that it formed more vigorously in the deep past, that a billion years or more are required to build up an observable volatile-rich layer, or that strong, ancient lithosphere is required to support an inherently weak, volatilized layer.

UNAVCO Real-Time GNSS Positioning: High-Precision Static and Kinematic Testing of the Next Generation GNSS network.

NASA Astrophysics Data System (ADS)

Berglund, H. T.; Hodgkinson, K. M.; Blume, F.; Mencin, D.; Phillips, D. A.; Meertens, C. M.; Mattioli, G. S.

2014-12-01

The GAGE Facility, managed by UNAVCO, operates a real-time GNSS (RT-GNSS) network of ~450 stations. The majority of the streaming stations are part of the EarthScope Plate Boundary Observatory (PBO). Following community input from a real-time GNSS data products and formats meeting hosted by UNAVCO in Spring of 2011, UNAVCO now provides real-time PPP positions, and network solutions where practical, for all available stations using Trimble's PIVOT RTX server software and TrackRT. The UNAVCO real-time system has the potential to enhance our understanding of earthquakes, seismic wave propagation, volcanic eruptions, magmatic intrusions, movement of ice, landslides, and the dynamics of the atmosphere. Beyond the ever increasing applications in science and engineering, RT-GNSS has the potential to provide early warning of hazards to emergency managers, utilities, other infrastructure managers, first responders and others. Upgrades to the network include eight Trimble NetR9 GNSS receivers with GLONASS and receiver-based RTX capabilities and sixteen new co-located MEMS based accelerometers. These new capabilities will allow integration of GNSS and strong motion data to produce broad-spectrum waveforms improving Earthquake Early Warning systems. Controlled outdoor kinematic and static experiments provide a useful method for evaluating and comparing real-time systems. UNAVCO has developed a portable low-cost antenna actuator to characterize the kinematic performance of receiver- and server-based real-time positioning algorithms and identify system limitations. We have performed tests using controlled 1-d antenna motions and will present comparisons between these and other post-processed kinematic algorithms including GIPSY-OASIS and TRACK. In addition to kinematic testing, long-term static testing of Trimble's RTX service is ongoing at UNAVCO and will be used to characterize the stability of the position time-series produced by RTX. In addition, with the goal of characterizing stability and improving software and higher level products based on real-time and high frequency GNSS time series, we present an overview of the UNAVCO RT-GPS system, a comparison of the UNAVCO generated real-time, static and community data products, and an overview of available common data sets.

Crustal layering and gravity highs in the Midcontinent of North America - implications for the formation of the Illinois Basin

NASA Astrophysics Data System (ADS)

Gilbert, H. J.; Boschelli, J.; Pavlis, G. L.; Hamburger, M. W.; Marshak, S.; Chen, C.; Yang, X.; DeLucia, M. S.; Larson, T. H.; Rupp, J.

2017-12-01

The emerging picture of crustal and lithospheric structure beneath the North American cratonic platform resulting from recent increases in the resolution of seismic studies is revealing a scale of complexity and heterogeneity not previously recognized. Examples of novel images of the lithosphere allowed by this increased sampling come from the results of the OIINK project, an EarthScope FlexArray experiment. OIINK data provides new insight into tectonic relationships among the Reelfoot Rift, Ozark Plateau, Rough Creek Graben, and Illinois Basin. Making use of ambient-noise tomography from data recorded by the OIINK Array and surrounding stations we produced a new shear-wave velocity model of the region. This model indicates detailed variations in crustal wavespeeds align with the regional tectonic features. Beyond corroborating previous observations of high-speed material in the mid- to lower crust of the southern Illinois Basin, this new model demonstrates that these anomalous velocities extend continuously from the Reelfoot, beneath the Mississippi Embayment, into southern Indiana. This model also includes a separate area characterized by a similarly thickened layer of increased velocities in the middle and lower crust beneath the LaSalle Deformation Belt, a north-south band of faults and folds that runs along the axis of the Illinois Basin. At depths of about 20 km, the top of these areas of thickened high-velocity crust align with a midcrustal discontinuity identified by receiver functions. Additionally, the lateral extent of these structures correlates with regions of increased Bouguer gravity. If the high-velocity structures contain high-density material, this configuration provides an explanation for the source of these positive gravity anomalies. These observations support a model in which Late Proterozoic rifting beneath the region of the Illinois Basin provided an opportunity for high-density material to enter the crust as residuum from melt extraction. In turn, the negative buoyancy forces resulting from this high-density material could then contribute to subsidence in the Illinois Basin, emphasizing the potential for intracrationic basins to originate from failed rifts.

Electrical conductivity of the Cascadia subduction zone and implications for the plate interface

NASA Astrophysics Data System (ADS)

Livelybrooks, D.; Bedrosian, P.; Egbert, G. D.; Key, K.; Schultz, A.; Parris, B. A.; Yang, B.; Bowles-martinez, E.

2016-12-01

The Magnetotelluric Observations of Cascadia using a Huge Array (MOCHA) experiment resulted in the collection of 146 amphibious, long-period magnetotelluric stations acquired between 2012 and 2014. These data, supplemented with the previously-acquired CAFÉ, EMSLAB, SWORMT and EarthScope (MT) Transportable Array stations, have been interpreted to provide electrical conductivity models of Cascadia spanning from the trench eastward through the Cascades, and extending to about 150km depth. We have a particular interest in understanding the roles electrically-conductive, aqueous fluids play in Cascadia subduction processes at or near the plate interface, thus inversions of data are predisposed to accommodate an initially-resistive (McCrory et al. 2014) slab. Beginning at the mantle wedge corner, 3-D inversions reveal significant, latitudinal variation in the conductivity, with enhanced conductivity at 47oN and south at 42oN. Two-dimensional inversions at 44.5oN allowing for a step discontinuity at the Moho give two distinct zones of conductance, one at the MWC tip (c.f. Furukowa, 2009) and another further down-dip, with a conductivity `plume' directed eastwards. At depths of between 20-25km we image a latitudinally-discontinuous resistive lower crust immediately overlying resistive subducted slab. This implies a lack of free fluids near the plate interface. Krogstad et al. (2016) have analyzed historic uplift data and can model the presence of an inboard `secondary locked zone' near 44.5oN. One explanation for both observations—a down-dip, `pinned interface' that is shielding the traditionally-modeled off-shore locked zone from stress accumulation, would explain the paucity of seismicity observed off the north-central Oregon coast during the four-year Cascadia Initiative. At coastal longitudes a narrow, supra-slab conductive zone is imaged at 22km depth with a southern termination at 45oN. It is notable that some researchers place the inboard boundary of the (mostly off-shore) seismogenic zone as moving eastward and on-shore beginning north of 45oN. The thinner Coast Range crust is imaged as generally more conductive north of 46oN, which is consistent with higher permeabilities ascribed to the Crescent formation.

Rifting the continental lithosphere: case studies of the lithosphere-asthenosphere system in rifted settings across the western U.S. and in the southern East African Rift

NASA Astrophysics Data System (ADS)

Hopper, E.; Gaherty, J. B.; Shillington, D. J.

2016-12-01

Continental extension comes in many guises, often described in terms of two endmembers. Narrow rifting is typified by a rift valley narrower than lithospheric thickness (50-100 km), presumed to result in steep lateral changes in crustal and lithospheric topography; wide rifting by a broad zone (<1000 km) of normal faulting associated with much smaller topographic gradients. A type example for the former is the East African Rift Valley; for the latter, the Basin and Range in the western U.S.A. An important control on rift development is the state of the lithosphere: for example, its strength and thickness. We analyse common conversion point stacked Sp converted wave images of the lithosphere beneath rift systems in the contiguous U.S., both the wide Basin and Range, and narrow rift systems such as the Rio Grande Rift and Salton Trough. We use Sp waves recorded by EarthScope's Transportable Array and other available permanent and temporary broadband stations. Beneath the Basin and Range, we observe a very strong, shallow velocity decrease (the lithosphere-asthenosphere boundary, or LAB) that is relatively uniform over 100s of km. The strength of this feature indicates melt has ponded at this transition. We have not observed a clear relationship between lithospheric thickness beneath the Basin and Range, and total degree of extension, current extension rate, or age since surface volcanism. Beneath narrow rifts in the western U.S., however, more localised thinning of the lithosphere has been observed. We also compare these observations with seismic images of the Malawi Rift, at the southern end of the Western Branch of the East African Rift System, using broadband data acquired as part of the Study of Extension and MaGmatism in Malawi aNd Tanzania (SEGMeNT) experiment. The Malawi Rift is extending slowly in a magma-poor region of relatively strong lithosphere. We constrain the pattern of plate-scale extension by observations of crustal thinning, and image complex variations in deeper lithospheric structure.

Rifting the continental lithosphere: case studies of the lithosphere-asthenosphere system in rifted settings across the western U.S. and in the southern East African Rift

NASA Astrophysics Data System (ADS)

Hopper, E.; Gaherty, J. B.; Shillington, D. J.

2017-12-01

Continental extension comes in many guises, often described in terms of two endmembers. Narrow rifting is typified by a rift valley narrower than lithospheric thickness (50-100 km), presumed to result in steep lateral changes in crustal and lithospheric topography; wide rifting by a broad zone (<1000 km) of normal faulting associated with much smaller topographic gradients. A type example for the former is the East African Rift Valley; for the latter, the Basin and Range in the western U.S.A. An important control on rift development is the state of the lithosphere: for example, its strength and thickness. We analyse common conversion point stacked Sp converted wave images of the lithosphere beneath rift systems in the contiguous U.S., both the wide Basin and Range, and narrow rift systems such as the Rio Grande Rift and Salton Trough. We use Sp waves recorded by EarthScope's Transportable Array and other available permanent and temporary broadband stations. Beneath the Basin and Range, we observe a very strong, shallow velocity decrease (the lithosphere-asthenosphere boundary, or LAB) that is relatively uniform over 100s of km. The strength of this feature indicates melt has ponded at this transition. We have not observed a clear relationship between lithospheric thickness beneath the Basin and Range, and total degree of extension, current extension rate, or age since surface volcanism. Beneath narrow rifts in the western U.S., however, more localised thinning of the lithosphere has been observed. We also compare these observations with seismic images of the Malawi Rift, at the southern end of the Western Branch of the East African Rift System, using broadband data acquired as part of the Study of Extension and MaGmatism in Malawi aNd Tanzania (SEGMeNT) experiment. The Malawi Rift is extending slowly in a magma-poor region of relatively strong lithosphere. We constrain the pattern of plate-scale extension by observations of crustal thinning, and image complex variations in deeper lithospheric structure.

Box Tomography: first application to the imaging of upper-mantle shear velocity and radial anisotropy structure beneath the North American continent

NASA Astrophysics Data System (ADS)

Clouzet, P.; Masson, Y.; Romanowicz, B.

2018-06-01

The EarthScope Transpotable Array (TA) deployment provides dense array coverage throughout the continental United States and with it, the opportunity for high-resolution 3-D seismic velocity imaging of the stable part of the North American (NA) upper mantle. Building upon our previous long-period waveform tomographic modeling, we present a higher resolution 3-D isotropic and radially anisotropic shear wave velocity model of the NA lithosphere and asthenosphere. The model is constructed using a combination of teleseismic and regional waveforms down to 40 s period and wavefield computations are performed using the spectral element method both for regional and teleseismic data. Our study is the first tomographic application of `Box Tomography', which allows us to include teleseismic events in our inversion, while computing the teleseismic wavefield only once, thus significantly reducing the numerical computational cost of several iterations of the regional inversion. We confirm the presence of high-velocity roots beneath the Archean part of the continent, reaching 200-250 km in some areas, however the thickness of these roots is not everywhere correlated to the crustal age of the corresponding cratonic province. In particular, the lithosphere is thick (˜250 km) in the western part of the Superior craton, while it is much thinner (˜150 km) in its eastern part. This may be related to a thermomechanical erosion of the cratonic root due to the passage of the NA plate over the Great Meteor hotspot during the opening of the Atlantic ocean 200-110 Ma. Below the lithosphere, an upper-mantle low-velocity zone (LVZ) is present everywhere under the NA continent, even under the thickest parts of the craton, although it is less developed there. The depth of the minimum in shear velocity has strong lateral variations, whereas the bottom of the LVZ is everywhere relatively flat around 270-300 km depth, with minor undulations of maximum 30 km that show upwarping under the thickest lithosphere and downwarping under tectonic regions, likely reflecting residual temperature anomalies. The radial anisotropy structure is less well resolved, but shows distinct signatures in highly deformed regions of the lithosphere.

Imaging Ancient Sutures with EarthScope Transportable Array Magnetotelluric Data

NASA Astrophysics Data System (ADS)

Egbert, G. D.

2014-12-01

Magnetotellurics (MT) provides a powerful geophysical tool for imaging of ancient suture zones, which are frequently marked by elongated zones of very low resistivity. These conductive anomalies, which can extend to great depths and have apparently persisted for several billion years, most likely result from graphite and sulfides deeply emplaced and remobilized, through subduction, accretion and orogenesis. The Earthscope MT transportable array provides a unique broad-scale view of sutures in the continental US. In the northwestern US subvertical conductive features bound all of the major cratonic blocks. These can be identified with the Cheyenne Belt between the Wyoming Craton (WC) and Yavapai Terranes (YT), the Great Falls Tectonic Zone between WC and the Medicine Hat Block (MHB), and the Vulcan Structure of southern Alberta between MHB and the Hearne Craton. In all cases the conductive anomalies extend well into the mantle lithosphere. The more recent MT TA footprint in the north-central US (surrounding the Mid-Continent Rift (MCR)) also reveals conductive signatures of ancient sutures. The most prominent lies south of Lake Superior, just north of the Niagara Fault (NF), and can be associated with the Penokean Orogeny (~1.85 Ga). A second, further south beneath Iowa and western Wisconsin, just south of the Spirit Lake tectonic zone (SLtz), can be identified with YT accretion (~1.75 Ga). Both of these sutures are cleanly cut by the MCR. The break in the anomalies is narrow (comparable to the surface expression of the MCR) indicating that rifting impacts on the entire crustal section were highly localized. The south-dipping NF conductive anomaly extends from surface outcrop to at least the Moho. The SLtz anomaly is north-dipping, extending from mid-crust through the Moho. In both cases there is some evidence for a modestly conductive layer (likely carbon) thrust to mid-lithospheric depths within the overriding terrane.

Supporting EarthScope Cyber-Infrastructure with a Modern GPS Science Data System

NASA Astrophysics Data System (ADS)

Webb, F. H.; Bock, Y.; Kedar, S.; Jamason, P.; Fang, P.; Dong, D.; Owen, S. E.; Prawirodirjo, L.; Squibb, M.

2008-12-01

Building on NASA's investment in the measurement of crustal deformation from continuous GPS, we are developing and implementing a Science Data System (SDS) that will provide mature, long-term Earth Science Data Records (ESDR's). This effort supports NASA's Earth Surface and Interiors (ESI) focus area and provide NASA's component to the EarthScope PBO. This multi-year development is sponsored by NASA's Making Earth System data records for Use in Research Environments (MEaSUREs) program. The SDS integrates the generation of ESDRs with data analysis and exploration, product generation, and modeling tools based on daily GPS data that include GPS networks in western North America and a component of NASA's Global GPS Network (GGN) for terrestrial reference frame definition. The system is expandable to multiple regional and global networks. The SDS builds upon mature data production, exploration, and analysis algorithms developed under NASA's REASoN, ACCESS, and SENH programs. This SDS provides access to positions, time series, velocity fields, and strain measurements derived from continuous GPS data obtained at tracking stations in both the Plate Boundary Observatory and other regional Western North America GPS networks, dating back to 1995. The SDS leverages the IT and Web Services developments carried out under the SCIGN/REASoN and ACCESS projects, which have streamlined access to data products for researchers and modelers, and which have created a prototype an on-the-fly interactive research environment through a modern data portal, GPS Explorer. This IT system has been designed using modern IT tools and principles in order to be extensible to any geographic location, scale, natural hazard, and combination of geophysical sensor and related data. We have built upon open GIS standards, particularly those of the OGC, and have used the principles of Web Service-based Service Oriented Architectures to provide scalability and extensibility to new services and capabilities.

Installation of EarthScope Borehole Strainmeters in Turkey to complement GONAF.

NASA Astrophysics Data System (ADS)

Johnson, W.; Gottlieb, M. H.; Mencin, D.; Van Boskirk, E.; Ozener, H.; Bohnhoff, M.; Bulut, F.; Bal, O.; Acarel, D.; Aydin, H.; Mattioli, G. S.

2015-12-01

Twice in the past 1000 years a sequence of damaging earthquakes has propagated over a period of a few decades along the North Anatolian Fault (NAF) in Turkey towards Istanbul, with the final earthquake in the sequence catastrophically damaging the city. This occurred most recently in 1509, causing 10,000 casualties in a population of about 200,000. The population is now 20 million, the building stock more fragile, and the last earthquake of the current sequence is considered imminent. Since July 2014, UNAVCO has installed 2 EarthScope borehole geophysical instrument strings, which include Gladwin Tensor strainmeters and passive, short-period 3-component seismometers, into boreholes provided by internationally supported Geophysical Observatory at the North Anatolian Fault (GONAF) and Bogazici University Kandilli Observatory. Funding for instruments and staff participation was provided by NSF. If the project remains on schedule, we anticipate that 4 additional BSM strings will be installed by the fall 2015. Our joint international project gives an opportunity to enhance the detection capability of a suite of deep seismometers (GONAF) installed near Istanbul and will permit us to image dynamic rupture along the NAF and to monitor and better understand the tectonic processes leading to failure. The tectonic and geodynamic environment of the NAF near Istanbul in many ways resembles the San Andreas Fault setting of San Francisco; these instruments will enhance the ability to monitor ultra-slow process near the probable source zone of the Mw>7 earthquake beneath the Marmara Sea on the NAF This project has provided UNAVCO an opportunity to gain experience in strainmeters installations outside of North America. The techniques developed to adapt to the challenges of installing borehole strainmeters on islands and other remote locations with limited resources will greatly enhance our ability to install these BSM instruments in similar locations in the future.

The EarthScope Plate Boundary Observatory and allied networks, the makings of nascent Earthquake and Tsunami Early Warning System in Western North America.

NASA Astrophysics Data System (ADS)

Mattioli, Glen; Mencin, David; Hodgkinson, Kathleen; Meertens, Charles; Phillips, David; Blume, Fredrick; Berglund, Henry; Fox, Otina; Feaux, Karl

2016-04-01

The NSF-funded GAGE Facility, managed by UNAVCO, operates approximately ~1300 GNSS stations distributed across North and Central America and in the circum-Caribbean. Following community input starting in 2011 from several workshops and associated reports,UNAVCO has been exploring ways to increase the capability and utility of the geodetic resources under its management to improve our understanding in diverse areas of geophysics including properties of seismic, volcanic, magmatic and tsunami deformation sources. Networks operated by UNAVCO for the NSF have the potential to profoundly transform our ability to rapidly characterize events, provide rapid characterization and warning, as well as improve hazard mitigation and response. Specific applications currently under development include earthquake early warning, tsunami early warning, and tropospheric modeling with university, commercial, non-profit and government partners on national and international scales. In the case of tsunami early warning, for example, an RT-GNSS network can provide multiple inputs in an operational system starting with rapid assessment of earthquake sources and associated deformation, which leads to the initial model of ocean forcing and tsunami generation. In addition, terrestrial GNSScan provide direct measurements of the tsunami through the associated traveling ionospheric disturbance from several 100's of km away as they approach the shoreline,which can be used to refine tsunami inundation models. Any operational system like this has multiple communities that rely on a pan-Pacific real-time open data set. Other scientific and operational applications for high-rate GPS include glacier and ice sheet motions, tropospheric modeling, and better constraints on the dynamics of space weather. Combining existing data sets and user communities, for example seismic data and tide gauge observations, with GNSS and Met data products has proven complicated because of issues related to metadata, appropriate data formats, data quality assessment in real-time and other issues related to using these products operational forecasting. While progress has been made toward more open and free data access across national borders and toward more cooperation among cognizant government sanctioned "early warning" agencies, some impediments remain making a truly operational system a work in progress. Accordingly, UNAVCO has embarked on significant improvements and improvement goals to the original infrastructure and scope of the PBO. We anticipate that PBO and related networks will form a backbone for these disparate efforts providing high quality, low latency raw and processed GNSS data. This requires substantial upgrades to the entire system from the basic GNNS receiver, through robust data collection, archiving and open distribution mechanisms, to efficient data-processing strategies. UNAVCO is currently in a partnership with the commercial and scientific stakeholders to define, develop and deploy all segments of this improved geodetic network. We present the overarching goals, and current and planned future stateof this international resource.

Looking beneath Snake River Plain using gravity and magnetic methods Murari Khatiwada and G. Randy Keller, ConocoPhillips School of Geology and Geophysics, University of Oklahoma, Norman, OK 73069

NASA Astrophysics Data System (ADS)

Khatiwada, M.; Keller, G.

2010-12-01

Tectonic evolution and structural complexities of the Snake River Plain (SRP), the role of extension in its formation, and the effects of the YellowStone (YS) hotspot track have been a topic of scientific discussion for decades. In this research, we are addressing some of these issues by focusing on the Western Snake River Plain (WRSP) using a pre-existing gravity and magnetic database compiled through a community effort. These data are available at the Pan American Center for Environmental studies (http://research.utep.edu/paces). In the regional context of the SRP, the Complete Bouguer Anomaly (CBA) ranges by about 210 mGal with the highest value in the vicinity of the WRSP. We used upward continuation filters, bandpass filters, and directional derivative filters to delineate features by wavelength and trend. Total Magnetic Intensity (TMI) was also analyzed. The magnetic intensity ranges over 600 nT with much more complex and erratic magnetic signatures that arise from the shallow basalt and rhyolite deposits within the region. We used pseudogravity and tilt derivative filters for further processing of the magnetic data. We are able to identify the major structural components in the area using gravity and magnetic data and their processing. The bounding normal faults of the WSRP are well observed. We constructed an axial gravity profile along the SRP starting at Walla Walla, Washington and extending through Yellowstone to Reygate, Montana. CBA values along this profile show that the western and central sections of the SPR have higher gravity anomaly values than the eastern sections and the YS area. We used forward gravity modeling of the subsurface structures across the WSRP starting from the Basin and Range province on the southwest to the Atlanta Lobe of the Idaho Batholith on the northeast. From the model, we observed that the Moho depth increases northeastward and varies between 30 and 46 km along the profile. These results match with receiver function Moho depth estimates from the EARTHSCOPE US Array. We used borehole data and shallow seismic survey results to constrain the upper 5 km of the model along the profile. A number of normal faults that form a series of grabens and half grabens were also modeled beneath the SRP. The gravity profile suggests that a higher density mafic intrusive body of about 8-10 km thickness lies directly beneath the WSRP. This body is possibly a mafic intrusion into the upper crust or could be a region of the middle and upper crust that was extensively intruded by sills and dikes during the time of extension in the area. This result agrees with other scientific results in the eastern SRP based on seismic data. On the southwest part of the WSRP profile, the Idaho-Oregon graben that separates the WSRP from the High Lava Plains was also modeled.

Terrestrial Real-Time Volcano Monitoring

NASA Astrophysics Data System (ADS)

Franke, M.

2013-12-01

As volcano monitoring involves more and different sensors from seismic to GPS receivers, from video and thermal cameras to multi-parameter probes measuring temperature, ph values and humidity in the ground and the air, it becomes important to design real-time networks that integrate and leverage the multitude of available parameters. In order to do so some simple principles need to be observed: a) a common time base for all measurements, b) a packetized general data communication protocol for acquisition and distribution, c) an open and well documented interface to the data permitting standard and emerging innovative processing, and d) an intuitive visualization platform for scientists and civil defense personnel. Although mentioned as simple principles, the list above does not necessarily lead to obvious solutions or integrated systems, which is, however, required to take advantage of the available data. Only once the different data streams are put into context to each other in terms of time and location can a broader view be obtained and additional information extracted. The presentation is a summary of currently available technologies and how they can achieve the goal of an integrated real-time volcano monitoring system. A common time base are standard for seismic and GPS networks. In different projects we extended this to video feeds and time-lapse photography. Other probes have been integrated with vault interface enclosures (VIE) as used in the Transportable Array (TA) of the USArray. The VIE can accommodate the sensors employed in volcano monitoring. The TA has shown that Antelope is a versatile and robust middleware. It provides the required packetized general communication protocol that is independent from the actual physical communication link leaving the network design to adopt appropriate and possible hybrid solutions. This applies for the data acquisition and the data/information dissemination providing both a much needed collaboration platform, as well as, system hardening backup centers. Moreover, Antelope, as typical middleware, allows the scientist and software developer to focus on the specific purpose of their application by providing well defined input/output interfaces. This will spur the development of original and inventive real-time processing schemes in the realm of volcano monitoring. Whatever the underlying data and information engine is, it is only as good as the frontend. Such a frontend has to accommodate the dual purpose of putting data and information in a form that is conducive for scientist and the emergency responder. Current projects in Italy and Abu Dhabi with multiple display centers gave us insights into how difficult it is to develop a multipurpose situation room. Currently, we are experimenting with sophisticated emergency management software that ties strong-motion measurement, structural behavior, and loss estimation to a situation-driven response plan. Although different in content and timeline, this can be adapted for developing volcano eruptions. A final word on remote sensing data, e.g. infrared imaging from an airplane: If the data can be streamed, there is a way to time tag them and include them in the broader real-time process. At least, batch processing should be considered in order to improve the overall information status pre- or post-event.

Towards an accurate real-time locator of infrasonic sources

NASA Astrophysics Data System (ADS)

Pinsky, V.; Blom, P.; Polozov, A.; Marcillo, O.; Arrowsmith, S.; Hofstetter, A.

2017-11-01

Infrasonic signals propagate from an atmospheric source via media with stochastic and fast space-varying conditions. Hence, their travel time, the amplitude at sensor recordings and even manifestation in the so-called "shadow zones" are random. Therefore, the traditional least-squares technique for locating infrasonic sources is often not effective, and the problem for the best solution must be formulated in probabilistic terms. Recently, a series of papers has been published about Bayesian Infrasonic Source Localization (BISL) method based on the computation of the posterior probability density function (PPDF) of the source location, as a convolution of a priori probability distribution function (APDF) of the propagation model parameters with likelihood function (LF) of observations. The present study is devoted to the further development of BISL for higher accuracy and stability of the source location results and decreasing of computational load. We critically analyse previous algorithms and propose several new ones. First of all, we describe the general PPDF formulation and demonstrate that this relatively slow algorithm might be among the most accurate algorithms, provided the adequate APDF and LF are used. Then, we suggest using summation instead of integration in a general PPDF calculation for increased robustness, but this leads us to the 3D space-time optimization problem. Two different forms of APDF approximation are considered and applied for the PPDF calculation in our study. One of them is previously suggested, but not yet properly used is the so-called "celerity-range histograms" (CRHs). Another is the outcome from previous findings of linear mean travel time for the four first infrasonic phases in the overlapping consecutive distance ranges. This stochastic model is extended here to the regional distance of 1000 km, and the APDF introduced is the probabilistic form of the junction between this travel time model and range-dependent probability distributions of the phase arrival time picks. To illustrate the improvements in both computation time and location accuracy achieved, we compare location results for the new algorithms, previously published BISL-type algorithms and the least-squares location technique. This comparison is provided via a case study of different typical spatial data distributions and statistical experiment using the database of 36 ground-truth explosions from the Utah Test and Training Range (UTTR) recorded during the US summer season at USArray transportable seismic stations when they were near the site between 2006 and 2008.

Seismic risk assessment and application in the central United States

USGS Publications Warehouse

Wang, Z.

2011-01-01

Seismic risk is a somewhat subjective, but important, concept in earthquake engineering and other related decision-making. Another important concept that is closely related to seismic risk is seismic hazard. Although seismic hazard and seismic risk have often been used interchangeably, they are fundamentally different: seismic hazard describes the natural phenomenon or physical property of an earthquake, whereas seismic risk describes the probability of loss or damage that could be caused by a seismic hazard. The distinction between seismic hazard and seismic risk is of practical significance because measures for seismic hazard mitigation may differ from those for seismic risk reduction. Seismic risk assessment is a complicated process and starts with seismic hazard assessment. Although probabilistic seismic hazard analysis (PSHA) is the most widely used method for seismic hazard assessment, recent studies have found that PSHA is not scientifically valid. Use of PSHA will lead to (1) artifact estimates of seismic risk, (2) misleading use of the annual probability of exccedance (i.e., the probability of exceedance in one year) as a frequency (per year), and (3) numerical creation of extremely high ground motion. An alternative approach, which is similar to those used for flood and wind hazard assessments, has been proposed. ?? 2011 ASCE.

Passive seismic imaging based on seismic interferometry: method and its application to image the structure around the 2013 Mw6.6 Lushan earthquake

NASA Astrophysics Data System (ADS)

Gu, N.; Zhang, H.

2017-12-01

Seismic imaging of fault zones generally involves seismic velocity tomography using first arrival times or full waveforms from earthquakes occurring around the fault zones. However, in most cases seismic velocity tomography only gives smooth image of the fault zone structure. To get high-resolution structure of the fault zones, seismic migration using active seismic data needs to be used. But it is generally too expensive to conduct active seismic surveys, even for 2D. Here we propose to apply the passive seismic imaging method based on seismic interferometry to image fault zone detailed structures. Seismic interferometry generally refers to the construction of new seismic records for virtual sources and receivers by cross correlating and stacking the seismic records on physical receivers from physical sources. In this study, we utilize seismic waveforms recorded on surface seismic stations for each earthquake to construct zero-offset seismic record at each earthquake location as if there was a virtual receiver at each earthquake location. We have applied this method to image the fault zone structure around the 2013 Mw6.6 Lushan earthquake. After the occurrence of the mainshock, a 29-station temporary array is installed to monitor aftershocks. In this study, we first select aftershocks along several vertical cross sections approximately normal to the fault strike. Then we create several zero-offset seismic reflection sections by seismic interferometry with seismic waveforms from aftershocks around each section. Finally we migrate these zero-offset sections to create seismic structures around the fault zones. From these migration images, we can clearly identify strong reflectors, which correspond to major reverse fault where the mainshock occurs. This application shows that it is possible to image detailed fault zone structures with passive seismic sources.

Dominant seismic sources for the cities in South Sumatra

NASA Astrophysics Data System (ADS)

Sunardi, Bambang; Sakya, Andi Eka; Masturyono, Murjaya, Jaya; Rohadi, Supriyanto; Sulastri, Putra, Ade Surya

2017-07-01

Subduction zone along west of Sumatra and Sumatran fault zone are active seismic sources. Seismotectonically, South Sumatra could be affected by earthquakes triggered by these seismic sources. This paper discussed contribution of each seismic source to earthquake hazards for cities of Palembang, Prabumulih, Banyuasin, OganIlir, Ogan Komering Ilir, South Oku, Musi Rawas and Empat Lawang. These hazards are presented in form of seismic hazard curves. The study was conducted by using Probabilistic Seismic Hazard Analysis (PSHA) of 2% probability of exceedance in 50 years. Seismic sources used in analysis included megathrust zone M2 of Sumatra and South Sumatra, background seismic sources and shallow crustal seismic sources consist of Ketaun, Musi, Manna and Kumering faults. The results of the study showed that for cities relatively far from the seismic sources, subduction / megathrust seismic source with a depth ≤ 50 km greatly contributed to the seismic hazard and the other areas showed deep background seismic sources with a depth of more than 100 km dominate to seismic hazard respectively.

Co-seismic slip, post-seismic slip, and largest aftershock associated with the 1994 Sanriku-haruka-oki, Japan, earthquake

NASA Astrophysics Data System (ADS)

Yagi, Yuji; Kikuchi, Masayuki; Nishimura, Takuya

2003-11-01

We analyzed continuous GPS data to investigate the spatio-temporal distribution of co-seismic slip, post-seismic slip, and largest aftershock associated with the 1994 Sanriku-haruka-oki, Japan, earthquake (Mw = 7.7). To get better resolution for co-seismic and post-seismic slip distribution, we imposed a weak constraint as a priori information of the co-seismic slip determined by seismic wave analyses. We found that the post-seismic slip during 100 days following the main-shock amount to as much moment release as the main-shock, and that the sites of co-seismic slip and post-seismic slip are partitioning on a plate boundary region in complimentary fashion. The major post-seismic slip was triggered by the mainshock in western side of the co-seismic slip, and the extent of the post-seismic slip is almost unchanged with time. It rapidly developed a shear stress concentration ahead of the slip area, and triggered the largest aftershock.

Decadal GPS Time Series and Velocity Fields Spanning the North American Continent and Beyond: New Data Products, Cyberinfrastructure and Case Studies from the EarthScope Plate Boundary Observatory (PBO) and Other Regional Networks

NASA Astrophysics Data System (ADS)

Phillips, D. A.; Herring, T.; Melbourne, T. I.; Murray, M. H.; Szeliga, W. M.; Floyd, M.; Puskas, C. M.; King, R. W.; Boler, F. M.; Meertens, C. M.; Mattioli, G. S.

2017-12-01

The Geodesy Advancing Geosciences and EarthScope (GAGE) Facility, operated by UNAVCO, provides a diverse suite of geodetic data, derived products and cyberinfrastructure services to support community Earth science research and education. GPS data and products including decadal station position time series and velocities are provided for 2000+ continuous GPS stations from the Plate Boundary Observatory (PBO) and other networks distributed throughout the high Arctic, North America, and Caribbean regions. The position time series contain a multitude of signals in addition to the secular motions, including coseismic and postseismic displacements, interseismic strain accumulation, and transient signals associated with hydrologic and other processes. We present our latest velocity field solutions, new time series offset estimate products, and new time series examples associated with various phenomena. Position time series, and the signals they contain, are inherently dependent upon analysis parameters such as network scaling and reference frame realization. The estimation of scale changes for example, a common practice, has large impacts on vertical motion estimates. GAGE/PBO velocities and time series are currently provided in IGS (IGb08) and North America (NAM08, IGb08 rotated to a fixed North America Plate) reference frames. We are reprocessing all data (1996 to present) as part of the transition from IGb08 to IGS14 that began in 2017. New NAM14 and IGS14 data products are discussed. GAGE/PBO GPS data products are currently generated using onsite computing clusters. As part of an NSF funded EarthCube Building Blocks project called "Deploying MultiFacility Cyberinfrastructure in Commercial and Private Cloud-based Systems (GeoSciCloud)", we are investigating performance, cost, and efficiency differences between local computing resources and cloud based resources. Test environments include a commercial cloud provider (Amazon/AWS), NSF cloud-like infrastructures within XSEDE (TACC, the Texas Advanced Computing Center), and in-house cyberinfrastructures. Preliminary findings from this effort are presented. Web services developed by UNAVCO to facilitate the discovery, customization and dissemination of GPS data and products are also presented.

Increasing tsunami preparedness through educator professional development in coastal Cascadia communities

NASA Astrophysics Data System (ADS)

Pratt-Sitaula, B. A.; Butler, R. F.; Hunter, N.; Lillie, R. J.; Magura, B.; Groom, R.; Johnson, J. A.; Coe, M.

2016-12-01

Increasing society's ability to mitigate risks is one of the major goals of geohazard research. Therefore part of tsunami science research must be finding effective ways to communicate scientific findings to the public to be used in community preparedness plans. The "Cascadia EarthScope Earthquake and Tsunami Education Program" (CEETEP; ceetep.oregonstate.edu) has worked to bridge the gap between scientific researchers and the public by providing professional development workshops for educators from coastal communities in Oregon, Washington, and northern California. CEETEP translates cutting edge EarthScope and other geoscience research into educational resources appropriate for K-12 teachers, park and museum interpreters, and emergency management outreach educators and their learners. Local educators have the potential to reach a wide segment of coastal residents. The tsunami generated by the next Great Cascadia Subduction Zone earthquake will arrive only 10-30 minutes after shaking, making mitigation and community-wide education an imperative. An essential component of CEETEP is collaboration with experts in science, pedagogy, and emergency preparedness. CEETEP provided two 4-day workshops and a follow-up Share-a-thon each year for three years (2013-2015). 151 educators participated in the program. Results from CEETEP are very encouraging. Participant content knowledge improved from 49% to 82% over the course of the workshop. Similarly, confidence in teaching about workshop topics increased from an average of 3.0 to 5.3 on a 6-point scale. Participant optimism about the efficacy and tractability of community-level planning also increased from 6.1 to 7.8 on a 9-point scale. Nearly 90% of participants continued to be active with the program through their March Share-a-thon and presented on a wide range of activities that they and their learners undertook related to earthquake and tsunami science and preparedness. Participants were also quite favorable about the innovative design of combining formal and informal educators into a single workshop. On a 6-point scale, they rated this professional exchange 5.5 for effectiveness. In all, the format and accomplishments of CEETEP can serve as a model for tsunami researchers interested in collaborating on outreach efforts.

WEB-IS2: Next Generation Web Services Using Amira Visualization Package

NASA Astrophysics Data System (ADS)

Yang, X.; Wang, Y.; Bollig, E. F.; Kadlec, B. J.; Garbow, Z. A.; Yuen, D. A.; Erlebacher, G.

2003-12-01

Amira (www.amiravis.com) is a powerful 3-D visualization package and has been employed recently by the science and engineering communities to gain insight into their data. We present a new web-based interface to Amira, packaged in a Java applet. We have developed a module called WEB-IS/Amira (WEB-IS2), which provides web-based access to Amira. This tool allows earth scientists to manipulate Amira controls remotely and to analyze, render and view large datasets over the internet, without regard for time or location. This could have important ramifications for GRID computing. The design of our implementation will soon allow multiple users to visually collaborate by manipulating a single dataset through a variety of client devices. These clients will only require a browser capable of displaying Java applets. As the deluge of data continues, innovative solutions that maximize ease of use without sacrificing efficiency or flexibility will continue to gain in importance, particularly in the Earth sciences. Major initiatives, such as Earthscope (http://www.earthscope.org), which will generate at least a terabyte of data daily, stand to profit enormously by a system such as WEB-IS/Amira (WEB-IS2). We discuss our use of SOAP (Livingston, D., Advanced SOAP for Web development, Prentice Hall, 2002), a novel 2-way communication protocol, as a means of providing remote commands, and efficient point-to-point transfer of binary image data. We will present our initial experiences with the use of Naradabrokering (www.naradabrokering.org) as a means to decouple clients and servers. Information is submitted to the system as a published item, while it is retrieved through a subscription mechanisms, via what is known as "topics". These topic headers, their contents, and the list of subscribers are automatically tracked by Naradabrokering. This novel approach promises a high degree of fault tolerance, flexibility with respect to client diversity, and language independence for the services (Erlebacher, G., Yuen, D.A., and F. Dubuffet, Current trends and demands in visualization in the geosciences, Electron. Geosciences, 4, 2001).

Using EarthScope magnetotelluric data to improve the resilience of the US power grid: rapid predictions of geomagnetically induced currents

NASA Astrophysics Data System (ADS)

Schultz, A.; Bonner, L. R., IV

2016-12-01

Existing methods to predict Geomagnetically Induced Currents (GICs) in power grids, such as the North American Electric Reliability Corporation standard adopted by the power industry, require explicit knowledge of the electrical resistivity structure of the crust and mantle to solve for ground level electric fields along transmission lines. The current standard is to apply regional 1-D resistivity models to this problem, which facilitates rapid solution of the governing equations. The systematic mapping of continental resistivity structure from projects such as EarthScope reveals several orders of magnitude of lateral variations in resistivity on local, regional and continental scales, resulting in electric field intensifications relative to existing 1-D solutions that can impact GICs to first order. The computational burden on the ground resistivity/GIC problem of coupled 3-D solutions inhibits the prediction of GICs in a timeframe useful to protecting power grids. In this work we reduce the problem to applying a set of filters, recognizing that the magnetotelluric impedance tensors implicitly contain all known information about the resistivity structure beneath a given site, and thus provides the required relationship between electric and magnetic fields at each site. We project real-time magnetic field data from distant magnetic observatories through a robustly calculated multivariate transfer function to locations where magnetotelluric impedance tensors had previously been obtained. This provides a real-time prediction of the magnetic field at each of those points. We then project the predicted magnetic fields through the impedance tensors to obtain predictions of electric fields induced at ground level. Thus, electric field predictions can be generated in real-time for an entire array from real-time observatory data, then interpolated onto points representing a power transmission line contained within the array to produce a combined electric field prediction necessary for GIC prediction along that line. This method produces more accurate predictions of ground electric fields in conductively heterogeneous areas that are not limited by distance from the nearest observatory, while still retaining comparable computational speeds as existing methods.

On the Development of Multi-Hazard Early Warning Networks: Practical experiences from North and Central America.

NASA Astrophysics Data System (ADS)

Mencin, David; Hodgkinson, Kathleen; Braun, John; Meertens, Charles; Mattioli, Glen; Phillips, David; Blume, Fredrick; Berglund, Henry; Fox, Otina; Feaux, Karl

2015-04-01

The GAGE facility, managed by UNAVCO, maintains and operates about 1300 GNSS stations distributed across North and Central America as part of the EarthScope Plate Boundary Observatory (PBO) and the Continuously Operating Caribbean GPS Observational Network (COCONet). UNAVCO has upgraded about 450 stations in these networks to real-time and high-rate (RT-GNSS) and included surface meteorological instruments. The majority of these streaming stations are part of the PBO but also include approximately 50 RT-GNSS stations in the Caribbean and Central American region as part of the COCONet and TLALOCNet projects. Based on community input UNAVCO has been exploring ways to increase the capability and utility of these resources to improve our understanding in diverse areas of geophysics including seismic, volcanic, magmatic and tsunami deformation sources, extreme weather events such as hurricanes and storms, and space weather. The RT-GNSS networks also have the potential to profoundly transform our ability to rapidly characterize geophysical events, provide early warning, as well as improve hazard mitigation and response. Specific applications currently under development with university, commercial, non-profit and government collaboration on national and international scales include earthquake and tsunami early warning systems and near real-time tropospheric modeling of hurricanes and precipitable water vapor estimate assimilation. Using tsunami early warning as an example, an RT-GNSS network can provide multiple inputs in an operational system starting with rapid assessment of earthquake sources and associated deformation which informs the initial modeled tsunami. The networks can then can also provide direct measurements of the tsunami wave heights and propagation by tracking the associated ionospheric disturbance from several 100's of km away as the waves approaches the shoreline. These GNSS based constraints can refine the tsunami and inundation models and potentially mitigate hazards. Other scientific and operational applications for high-rate GPS include glacier and ice sheet motions, tropospheric modeling, and better constraints on the dynamics of space weather. Our operational system has multiple communities that use and depend on a Pan-Pacific real-time open data set. The ability to merge existing data sets and user communities, seismic and tide gauge observations, with GNSS and Met data products has proven complicated because of issues related to meta-data, appropriate data formats, data quality assessment in real-time and specific issues related to using these products in operational forecasting. Additional issues related to data access across national borders and cognizant government sanctioned "early warning" agencies, some committed to specific technologies, methodologies, internal structure and further constrained by data policies make a truly operational system an on-going work in progress. We present a short history of evolving a very large and expensive RT-GNSS network originally designed to answer specific long term scientific questions about structure and evolution of North American plate boundaries into a much needed national hazard system while continuing to serve our core community in long term scientific studies. Out primary focus in this presentation is an analysis of our current goals and impediments to achieving these broader objectives.

Scientific Drilling in the Snake River Plain: Past, Present, and Future

NASA Astrophysics Data System (ADS)

Shervais, J. W.; Hanan, B. B.; Hughes, S. S.; Geist, D.; Vetter, S. K.

2006-12-01

The Snake River-Yellowstone volcanic province has long been linked to the concept of lithospheric drift over a fixed mantle thermal anomaly or hotspot. This concept is reinforced by seismic tomography that images this anomaly to depths around 500 km, but alternative proposals still present a serious challenge. Basaltic volcanism spans a significant age range and basaltic volcanism in the western SRP lies well off the hotspot track and cannot be related directly to the hotspot in any simple way. The plume-track age progression is documented by rhyolite volcanic centers, but even these represent extended time periods that overlap in age with adjacent centers. Scientific drilling projects carried out over the last two decades have made significant contributions to our understanding of both basaltic and rhyolitic volcanism associated with the Snake River-Yellowstone hotspot system. Because these drill holes also intercept sedimentary interbeds or, in the case of the western SRP, thick sections of Pliocene and Pleistocene sediments, they have also contributed to our understanding of basin formation by thermal collapse in the wake of the hotspot passage or by rifting, paleoclimate of the interior west, and groundwater systems in volcanic rocks. Many of these drill holes are associated with the Idaho National Laboratory (INL) in the eastern plain; others were drilled for geothermal or petroleum exploration. The latter include older holes that were not instrumented or logged in detail, but which still provide valuable stratigraphic controls. We focus here on the result of basalt drilling, which have been high-lighted in recent publications. Basaltic volcanism in the Snake River plain is dominated by olivine tholeiites that have major and trace element characteristics of ocean island basalt: the range in MgO is similar to MORB, but Ti, Fe, P, K, Sr, Zr and LREE/HREE ratios are all higher. Recent studies of basalts from the drill holes show that they evolved by fractionation in a mid-crustal sill complex that has been imaged seismically. Further, the chemical and isotopic systematics of these basalts require assimilation of consanguineous mafic material inferred to represent previously intruded sills. Major and trace element modeling suggest formation of the primary melts by melting of a source similar to E- MORB source. Trace element systematics document mixing between a plume-like source and a more depleted source that is not DMM. A similar more depleted source is inferred for Hawaii, suggesting that it is not continental lithosphere. Future scientific drilling in the SRP is the focus of Project HOTSPOT, a multi-disciplinary initiative that seeks to document time-space variations in the SRP-Yellowstone volcanic system. A workshop sponsored by the International Continental Drilling Program was held in May 2006 to develop a targeted program of scientific drilling that examines the entire plume-lithosphere system across a major lithospheric boundary, with holes targeting basalt, rhyolite, and sediments. These drill holes will complement geophysical studies of continental dynamics (e.g., Earthscope), as well as current studies centered on Yellowstone. Additional components of a targeted drilling program include studies of lacustrine sediments that document paleoclimate change in North America during the Pliocene—Pleistocene and fluid flow at deeper crustal levels.

Seismic hazard assessment: Issues and alternatives

USGS Publications Warehouse

Wang, Z.

2011-01-01

Seismic hazard and risk are two very important concepts in engineering design and other policy considerations. Although seismic hazard and risk have often been used inter-changeably, they are fundamentally different. Furthermore, seismic risk is more important in engineering design and other policy considerations. Seismic hazard assessment is an effort by earth scientists to quantify seismic hazard and its associated uncertainty in time and space and to provide seismic hazard estimates for seismic risk assessment and other applications. Although seismic hazard assessment is more a scientific issue, it deserves special attention because of its significant implication to society. Two approaches, probabilistic seismic hazard analysis (PSHA) and deterministic seismic hazard analysis (DSHA), are commonly used for seismic hazard assessment. Although PSHA has been pro-claimed as the best approach for seismic hazard assessment, it is scientifically flawed (i.e., the physics and mathematics that PSHA is based on are not valid). Use of PSHA could lead to either unsafe or overly conservative engineering design or public policy, each of which has dire consequences to society. On the other hand, DSHA is a viable approach for seismic hazard assessment even though it has been labeled as unreliable. The biggest drawback of DSHA is that the temporal characteristics (i.e., earthquake frequency of occurrence and the associated uncertainty) are often neglected. An alternative, seismic hazard analysis (SHA), utilizes earthquake science and statistics directly and provides a seismic hazard estimate that can be readily used for seismic risk assessment and other applications. ?? 2010 Springer Basel AG.

Bayesian identification of multiple seismic change points and varying seismic rates caused by induced seismicity

NASA Astrophysics Data System (ADS)

Montoya-Noguera, Silvana; Wang, Yu

2017-04-01

The Central and Eastern United States (CEUS) has experienced an abnormal increase in seismic activity, which is believed to be related to anthropogenic activities. The U.S. Geological Survey has acknowledged this situation and developed the CEUS 2016 1 year seismic hazard model using the catalog of 2015 by assuming stationary seismicity in that period. However, due to the nonstationary nature of induced seismicity, it is essential to identify change points for accurate probabilistic seismic hazard analysis (PSHA). We present a Bayesian procedure to identify the most probable change points in seismicity and define their respective seismic rates. It uses prior distributions in agreement with conventional PSHA and updates them with recent data to identify seismicity changes. It can determine the change points in a regional scale and may incorporate different types of information in an objective manner. It is first successfully tested with simulated data, and then it is used to evaluate Oklahoma's regional seismicity.

The UNAVCO Real-time GPS Data Processing System and Community Reference Data Sets

NASA Astrophysics Data System (ADS)

Sievers, C.; Mencin, D.; Berglund, H. T.; Blume, F.; Meertens, C. M.; Mattioli, G. S.

2013-12-01

UNAVCO has constructed a real-time GPS (RT-GPS) network of 420 GPS stations. The majority of the streaming stations come from the EarthScope Plate Boundary Observatory (PBO) through an NSF-ARRA funded Cascadia Upgrade Initiative that upgraded 100 backbone stations throughout the PBO footprint and 282 stations focused in the Pacific Northwest. Additional contributions from NOAA (~30 stations in Southern California) and the USGS (8 stations at Yellowstone) account for the other real-time stations. Based on community based outcomes of a workshop focused on real-time GPS position data products and formats hosted by UNAVCO in Spring of 2011, UNAVCO now provides real-time PPP positions for all 420 stations using Trimble's PIVOT software and for 50 stations using TrackRT at the volcanic centers located at Yellowstone (Figure 1 shows an example ensemble of TrackRT networks used in processing the Yellowstone data), Mt St Helens, and Montserrat. The UNAVCO real-time system has the potential to enhance our understanding of earthquakes, seismic wave propagation, volcanic eruptions, magmatic intrusions, movement of ice, landslides, and the dynamics of the atmosphere. Beyond its increasing uses for science and engineering, RT-GPS has the potential to provide early warning of hazards to emergency managers, utilities, other infrastructure managers, first responders and others. With the goal of characterizing stability and improving software and higher level products based on real-time GPS time series, UNAVCO is developing an open community standard data set where data processors can provide solutions based on common sets of RT-GPS data which simulate real world scenarios and events. UNAVCO is generating standard data sets for playback that include not only real and synthetic events but also background noise, antenna movement (e.g., steps, linear trends, sine waves, and realistic earthquake-like motions), receiver drop out and online return, interruption of communications (such as, bulk regional failures due to specific carriers during an actual event), satellites rising and setting, various constellation outages and differences in performance between real-time and simulated (retroactive) real-time. We present an overview of the UNAVCO RT-GPS system, a comparison of the UNAVCO generated real-time data products, and an overview of available common data sets.

NASA's DESDynI in Alaska

NASA Astrophysics Data System (ADS)

Sauber, J. M.; Hofton, M. A.; Bruhn, R. L.; Forster, R. R.; Burgess, E. W.; Cotton, M. M.

2010-12-01

In 2007 the National Research Council Earth Science Decadal Survey, Earth Science Applications from Space, recommended an integrated L-band InSAR and multibeam Lidar mission called DESDynI (Deformation, Ecosystem Structure, and Dynamics of Ice) and it is scheduled for launch in 2017. The NASA InSAR and Lidar mission is optimized for studying geohazards and global environmental change. The complex plate boundary in southern coastal Alaska provides an excellent setting for testing DESDynI capabilities to recover fundamental parameters of glacio-seismotectonic processes. Also, aircraft and satellites acquisitions of Lidar and L-band SAR have been made in this region in the last decade that can be used for DESDynI performance simulations. Since the Lidar observations would penetrate most vegetation, the accurate bald Earth elevation profiles will give new elevation information beyond the standard 30-m digital elevation models (DEM) and the Lidar-derived elevations will provide an accurate georeferenced surface for local and regional scale studies. In an earlier study we demonstrated how the Lidar observations could be used in combination with SAR to generate an improved InSAR derived DEM in the Barrow, Alaska region [Atwood et al., 2007]; here we discuss how Lidar could be fused with L-band SAR in more rugged, vegetated terrane. Based on simulations of multi-beam Lidar instrument performance over uplifted marine terraces, active faults and folds, uplift associated with the 1899 Yakataga seismic event (M=8), and elevation change on the glaciers in southern, coastal Alaska, we report on the significance of the DESDynI Lidar contiguous 25 m footprint elevation profiles for EarthScope related studies in Alaska. We are using the morphology and dynamics of glaciers derived from L-band SAR ice velocities to infer the large scale sub-ice structures that form the structural framework of the Seward-Bagley Basins. Using primarily winter acquisitions of L-band SAR data from ALOS/PALSAR (Mode: Fine beam, HH) we have been able to estimate ice velocities from offset-tracking in the Upper and Lower Seward Basin even though the acquisitions are 46 days apart. We anticipate with the shorter repeat time for DESDynI-SAR acquisitions that we will be able to estimate seasonal ice velocities over a larger range of regions within both the ablation and accumulation zones.

Using thermal and compositional modeling to assess the role of water in Alaskan flat slab subduction

NASA Astrophysics Data System (ADS)

Robinson, S. E.; Porter, R. C.; Hoisch, T. D.

2017-12-01

Although plate tectonic theory is well established in the geosciences, the mechanisms and details of various plate-tectonics related phenomena are not always well understood. In some ( 10%) convergent plate boundaries, subduction of downgoing oceanic plates is characterized by low angle geometries and is termed "flat slab subduction." The mechanism(s) driving this form of subduction are not well understood. The goal of this study is to explore the role that water plays in these flat slab subduction settings. This is important for a better understanding of the behavior of these systems and for assessing volcanic hazards associated with subduction and slab rollback. In southern Alaska, the Pacific Plate is subducting beneath the North American plate at a shallow angle. This low-angle subduction within the region is often attributed to the subduction of the Yakutat block, a terrane accreting to the south-central coast of Alaska. This flat slab region is bounded by the Aleution arc to the west and the strike-slip Queen Charlotte fault to the east. Temperature and compositional models for a 500-km transect across this subduction zone in Alaska were run for ten million years (the length of time that flat slab subduction has been ongoing in Alaska) and allow for interpretation of present-day conditions at depth. This allows for an evaluation of two hypotheses regarding the role of water in flat-slab regions: (1) slab hydration and dehydration help control slab buoyancy which influences whether flat slab subduction will be maintained or ended. (2) slab hydration/dehydration of the overlying lithosphere impacts deformation within the upper plate as water encourages plate deformation. Preliminary results from thermal modeling using Thermod8 show that cooling of the mantle to 500 °C is predicted down to 100 km depth at 10 million years after the onset of low-angle subduction (representing present-day). Results from compositional modeling in Perple_X show the maximum amount of water that can be held in the system assuming crustal (basalt and metabasalt) and mantle (peridotite) compositions. These models will be compared with seismic velocity models created from EarthScope Transportable Array data in the region in order to determine amounts of serpentinite and other water-bearing rocks within the flat slab subduction system.

Preparing the Plate Boundary Observatory GNSS Network for the Future

NASA Astrophysics Data System (ADS)

Austin, K. E.; Walls, C. P.; Dittman, T.; Mann, D.; Boyce, E. S.; Basset, A.; Woolace, A. C.; Turner, R.; Lawrence, S.; Rhoades, S.; Pyatt, C.; Willoughby, H.; Feaux, K.; Mattioli, G. S.

2017-12-01

The EarthScope Plate Boundary Observatory (PBO) GNSS network, funded by the NSF and operated by UNAVCO, is comprised of 1100 permanent GPS and GNSS stations spanning three principal tectonic regimes and is administered by distinct management. The GPS-only network was initially designed for daily data file downloads primarily for tectonic analysis. This low data volume requirement and circa-2004 IP-based cellular/VSat modems provided significant freedom for station placement and enabled science-targeted installation of stations in some of the most remote and geologically interesting areas. Community requests for high-rate data downloads for GNSS seismology, airborne LiDAR surveys, meteorological/GNSS/seismic real-time data flow and other demands, however, require significantly increased bandwidth beyond the 5-20 kB/s transfer rates that were needed as part of the original design. Since the close of construction in September 2008, PBO enhancements have been implemented through additional funding by the NSF (ARRA/Cascadia), NOAA, and NASA and in collaboration with stakeholders such as Caltrans, ODOT, Scripps, and the USGS. Today, only 18 of the original cell modems remain, with 601 upgraded cell modems providing 3G/4G/LTE data communications that support transfer rates ranging from 80-400 kB/s. Radio network expansion and upgrades continue to harden communications using both 2.4 GHz and 5.8 GHz radios. 78 VSAT and 5 manual download sites remain. PBO-wide the network capabilities for 1 Hz & 5 Hz downloads or low latency 1 Hz streaming are 85%, 80% and 65% of PBO stations, respectively, with 708 active 1 Hz streams. Vaisala meteorological instruments are located at 140 sites most of which stream GPS/Met data in real time. GPS-only receivers are being replaced with GNSS receivers and antennas. Today, there are 279 stations in the PBO network with either GLONASS enabled Trimble NetR9 or full GNSS constellation Septentrio PolaRx5 receivers. Just as the scale and geographical density of the PBO project has opened up new and unexpected avenues for geophysical research across disciplines (e.g. atmosphere, meteorology, snow pack, tides, vegetation growth, drought monitoring, etc.), the coming decade under the NGEO banner will undoubtedly present new opportunities as the network continues to be modernized.

Providing Hands on Experiences to Museum Visitors to Explore and Learn about Earthquakes and their Impacts in the Pacific Northwest

NASA Astrophysics Data System (ADS)

Olds, S. E.; Schiffman, C. R.; Butler, R. F.; Farley, M.; Frankel, S.; Hunter, N.; Lillie, R. J.

2013-12-01

Over the past ten years, UNAVCO has developed a suite of learning materials for formal undergraduate and grades 6-12 classroom environments, integrating GPS data from the EarthScope Plate Boundary Observatory (PBO) to explore Earth science processes. To make complex Earth processes accessible to general audiences, UNAVCO has designed a multi-component visiting museum exhibit that explores the tectonic setting of the United States Pacific Northwest, hazards of living on a plate boundary, and the technologies being used to study the plate motion and in the future, help communities become more resilient to the impacts of earthquakes. This exhibit was installed in Fall 2013 at the Oregon State University (OSU) Hatfield Marine Science Center (HMSC) in Newport, Oregon. Through multiple hands-on elements, visitors to the HMSC exhibit explore and experience the build up and release of strain in the region, along with some of the technologies used to measure these changes. In one component, visitors compress a model of the Pacific Northwest to feel the build up of strain in the landscape and observe the movement of land over time. Supporting panels connect this movement to the measurements currently being observed by the network of PBO and other GPS stations in the Pacific Northwest. In another component, visitors learn about the recurrence interval for earthquakes at the Juan De Fuca - North America plate boundary by turning a handle to slowly move and compress plates until a simulated earthquake occurs. A related component explores how an earthquake early warning system (EEWS) of the future might combine seismic data collected by both seismometers and real time GPS to allow people and communities time to prepare for oncoming ground shaking and tsunami after an earthquake. Several technologies are also highlighted throughout the exhibit, including information panels that compare the accuracy of high precision GPS with smartphone technologies. Additionally, models of a full-sized PBO GPS monument and power and communication systems demonstrate the technology supporting real-time GPS data acquisition and rapid data transfer required for current research and future EEWS centers. An accompanying interactive kiosk provides additional content. The presentation will provide more details about the exhibit components and preliminary visitor feedback.

Alaska Seismic Hazards Safety Commission

Science.gov Websites

State Employees ASHSC State of Alaska search Alaska Seismic Hazards Safety Commission View of Anchorage and Commissions Alaska Seismic Hazards Safety Commission (ASHSC) main contant Alaska Seismic Hazards Safety Commission logo Alaska Seismic Hazards Safety Commission (ASHSC) - Mission The Alaska Seismic

Regional Observation of Seismic Activity in Baekdu Mountain

NASA Astrophysics Data System (ADS)

Kim, Geunyoung; Che, Il-Young; Shin, Jin-Soo; Chi, Heon-Cheol

2015-04-01

Seismic unrest in Baekdu Mountain area between North Korea and Northeast China region has called attention to geological research community in Northeast Asia due to her historical and cultural importance. Seismic bulletin shows level of seismic activity in the area is higher than that of Jilin Province of Northeast China. Local volcanic observation shows a symptom of magmatic unrest in period between 2002 and 2006. Regional seismic data have been used to analyze seismic activity of the area. The seismic activity could be differentiated from other seismic phenomena in the region by the analysis.

Causality between expansion of seismic cloud and maximum magnitude of induced seismicity in geothermal field

NASA Astrophysics Data System (ADS)

Mukuhira, Yusuke; Asanuma, Hiroshi; Ito, Takatoshi; Häring, Markus

2016-04-01

Occurrence of induced seismicity with large magnitude is critical environmental issues associated with fluid injection for shale gas/oil extraction, waste water disposal, carbon capture and storage, and engineered geothermal systems (EGS). Studies for prediction of the hazardous seismicity and risk assessment of induced seismicity has been activated recently. Many of these studies are based on the seismological statistics and these models use the information of the occurrence time and event magnitude. We have originally developed physics based model named "possible seismic moment model" to evaluate seismic activity and assess seismic moment which can be ready to release. This model is totally based on microseismic information of occurrence time, hypocenter location and magnitude (seismic moment). This model assumes existence of representative parameter having physical meaning that release-able seismic moment per rock volume (seismic moment density) at given field. Seismic moment density is to be estimated from microseismic distribution and their seismic moment. In addition to this, stimulated rock volume is also inferred by progress of microseismic cloud at given time and this quantity can be interpreted as the rock volume which can release seismic energy due to weakening effect of normal stress by injected fluid. Product of these two parameters (equation (1)) provide possible seismic moment which can be released from current stimulated zone as a model output. Difference between output of this model and observed cumulative seismic moment corresponds the seismic moment which will be released in future, based on current stimulation conditions. This value can be translated into possible maximum magnitude of induced seismicity in future. As this way, possible seismic moment can be used to have feedback to hydraulic stimulation operation in real time as an index which can be interpreted easily and intuitively. Possible seismic moment is defined as equation (1), where D is seismic moment density (Mo/m3) and V stim is stimulated rock volume (m3). Mopossible = D ∗ V stim(1) We applied this conceptual model to real microseismic data set from Basel EGS project where several induced seismicity with large magnitude occurred and brought constructive damage. Using the hypocenter location determined by the researcher of Tohoku Univ., Japan and moment magnitude estimated from Geothermal Explorers Ltd., operating company, we were able to estimate reasonable seismic moment density meaning that one representative parameter exists and can characterize seismic activity at Basel at each time step. With stimulated rock volume which was also inferred from microseismic information, we estimated possible seismic moment and assess the difference with observed value. Possible seismic moment significantly increased after shut-in when the seismic cloud (stimulated zone) mostly progressed, resulting that the difference with the observed cumulative seismic moment automatically became larger. This suggests that there is moderate seismic moment which will be released in near future. In next few hours, the largest event actually occurred. Therefore, our proposed model was successfully able to forecast occurrence of the large events. Furthermore, best forecast of maximum magnitude was Mw 3 level and the largest event was Mw 3.41, showing reasonable performance in terms of quantitative forecast in magnitude. Our attempt to assess the seismic activity from microseismic information was successful and it also suggested magnitude release can be correlate with the expansion of seismic cloud as the definition of possible seismic moment model indicates. This relationship has been observed in microseismic observational study and several previous study also suggested their correlation with stress released rock volume. Our model showed harmonic results with these studies and provide practical method having clear physical meaning to assess the seismic activity in real time, based on microseismic data.

Final Report: Seismic Hazard Assessment at the PGDP

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Zhinmeng

2007-06-01

Selecting a level of seismic hazard at the Paducah Gaseous Diffusion Plant for policy considerations and engineering design is not an easy task because it not only depends on seismic hazard, but also on seismic risk and other related environmental, social, and economic issues. Seismic hazard is the main focus. There is no question that there are seismic hazards at the Paducah Gaseous Diffusion Plant because of its proximity to several known seismic zones, particularly the New Madrid Seismic Zone. The issues in estimating seismic hazard are (1) the methods being used and (2) difficulty in characterizing the uncertainties ofmore » seismic sources, earthquake occurrence frequencies, and ground-motion attenuation relationships. This report summarizes how input data were derived, which methodologies were used, and what the hazard estimates at the Paducah Gaseous Diffusion Plant are.« less

Seismic data are rich in information about subsurface formations and fluids

DOE Office of Scientific and Technical Information (OSTI.GOV)

Farfour, Mohammed; Yoon, Wang Jung; Kim, Dongshin

2016-06-08

Seismic attributes are defined as any measured or computed information derived from seismic data. Throughout the last decades extensive work has been done in developing variety of mathematical approaches to extract maximum information from seismic data. Nevertheless, geoscientists found that seismic is still mature and rich in information. In this paper a new seismic attribute is introduced. Instantaneous energy seismic attribute is an amplitude based attribute that has the potential to emphasize anomalous amplitude associated with hydrocarbons. Promising results have been obtained from applying the attribute on seismic section traversing hydrocarbon filled sand from Alberta, Canada.

Fast principal component analysis for stacking seismic data

NASA Astrophysics Data System (ADS)

Wu, Juan; Bai, Min

2018-04-01

Stacking seismic data plays an indispensable role in many steps of the seismic data processing and imaging workflow. Optimal stacking of seismic data can help mitigate seismic noise and enhance the principal components to a great extent. Traditional average-based seismic stacking methods cannot obtain optimal performance when the ambient noise is extremely strong. We propose a principal component analysis (PCA) algorithm for stacking seismic data without being sensitive to noise level. Considering the computational bottleneck of the classic PCA algorithm in processing massive seismic data, we propose an efficient PCA algorithm to make the proposed method readily applicable for industrial applications. Two numerically designed examples and one real seismic data are used to demonstrate the performance of the presented method.

Short-Period Seismic Noise in Vorkuta (Russia)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kishkina, S B; Spivak, A A; Sweeney, J J

Cultural development of new subpolar areas of Russia is associated with a need for detailed seismic research, including both mapping of regional seismicity and seismic monitoring of specific mining enterprises. Of special interest are the northern territories of European Russia, including shelves of the Kara and Barents Seas, Yamal Peninsula, and the Timan-Pechora region. Continuous seismic studies of these territories are important now because there is insufficient seismological knowledge of the area and an absence of systematic data on the seismicity of the region. Another task of current interest is the necessity to consider the seismic environment in the design,more » construction, and operation of natural gas extracting enterprises such as the construction of the North European Gas Pipeline. Issues of scientific importance for seismic studies in the region are the complex geodynamical setting, the presence of permafrost, and the complex tectonic structure. In particular, the Uralian Orogene (Fig. 1) strongly affects the propagation of seismic waves. The existing subpolar seismic stations [APA (67,57{sup o}N; 33,40{sup o}E), LVZ (67,90{sup o}N; 34,65{sup o}E), and NRIL (69,50{sup o}N; 88,40{sup o}E)] do not cover the extensive area between the Pechora and Ob Rivers (Fig. 1). Thus seismic observations in the Vorkuta area, which lies within the area of concern, represent a special interest. Continuous recording at a seismic station near the city of Vorkuta (67,50{sup o}N; 64,11{sup o}E) [1] has been conducted since 2005 for the purpose of regional seismic monitoring and, more specifically, detection of seismic signals caused by local mining enterprises. Current surveys of local seismic noise [7,8,9,11], are particularly aimed at a technical survey for the suitability of the site for installation of a small-aperture seismic array, which would include 10-12 recording instruments, with the Vorkuta seismic station as the central element. When constructed, this seismic array will considerably improve the recording capacity of regional and local seismic events. It will allow detection of signatures of seismic waves propagating in submeridional and sublatitudinal directions. The latter is of special interest not only to access the influence of the Urals on propagation patterns of seismic waves, but also to address other questions, such as the structure and dynamic characteristics of the internal dynamo of the Earth [9,13]. Recording seismic waves at low angular distances from seismically active subpolar zones will allow us to collect data on vortical and convective movements in subpolar lithosphere blocks and at the boundary of the inner core of the Earth, possibly giving essential clues to the modeling of the Earth's electromagnetic field [3,13]. The present study considers basic features of seismic noise at the Vorkuta station obtained through the analysis of seismic records from March, 2006 till December, 2007.« less

Natural regeneration on seismic lines influences movement behaviour of wolves and grizzly bears.

PubMed

Finnegan, Laura; Pigeon, Karine E; Cranston, Jerome; Hebblewhite, Mark; Musiani, Marco; Neufeld, Lalenia; Schmiegelow, Fiona; Duval, Julie; Stenhouse, Gordon B

2018-01-01

Across the boreal forest of Canada, habitat disturbance is the ultimate cause of caribou (Rangifer tarandus caribou) declines. Habitat restoration is a focus of caribou recovery efforts, with a goal to finding ways to reduce predator use of disturbances, and caribou-predator encounters. One of the most pervasive disturbances within caribou ranges in Alberta, Canada are seismic lines cleared for energy exploration. Seismic lines facilitate predator movement, and although vegetation on some seismic lines is regenerating, it remains unknown whether vegetation regrowth is sufficient to alter predator response. We used Light Detection and Ranging (LiDAR) data, and GPS locations, to understand how vegetation and other attributes of seismic lines influence movements of two predators, wolves (Canis lupus) and grizzly bears (Ursus arctos). During winter, wolves moved towards seismic lines regardless of vegetation height, while during spring wolves moved towards seismic lines with higher vegetation. During summer, wolves moved towards seismic lines with lower vegetation and also moved faster near seismic lines with vegetation <0.7 m. Seismic lines with lower vegetation height were preferred by grizzly bears during spring and summer, but there was no relationship between vegetation height and grizzly bear movement rates. These results suggest that wolves use seismic lines for travel during summer, but during winter wolf movements relative to seismic lines could be influenced by factors additional to movement efficiency; potentially enhanced access to areas frequented by ungulate prey. Grizzly bears may be using seismic lines for movement, but could also be using seismic lines as a source of vegetative food or ungulate prey. To reduce wolf movement rate, restoration could focus on seismic lines with vegetation <1 m in height. However our results revealed that seismic lines continue to influence wolf movement behaviour decades after they were built, and even at later stages of regeneration. Therefore it remains unknown at what stage of natural regeneration, if any, wolves cease to respond to seismic lines. To reduce wolf response to seismic lines, active restoration tactics like blocking seismic lines and tree planting, along with management of alternate prey, could be evaluated.

Natural regeneration on seismic lines influences movement behaviour of wolves and grizzly bears

PubMed Central

Pigeon, Karine E.; Cranston, Jerome; Hebblewhite, Mark; Musiani, Marco; Neufeld, Lalenia; Schmiegelow, Fiona; Duval, Julie; Stenhouse, Gordon B.

2018-01-01

Across the boreal forest of Canada, habitat disturbance is the ultimate cause of caribou (Rangifer tarandus caribou) declines. Habitat restoration is a focus of caribou recovery efforts, with a goal to finding ways to reduce predator use of disturbances, and caribou-predator encounters. One of the most pervasive disturbances within caribou ranges in Alberta, Canada are seismic lines cleared for energy exploration. Seismic lines facilitate predator movement, and although vegetation on some seismic lines is regenerating, it remains unknown whether vegetation regrowth is sufficient to alter predator response. We used Light Detection and Ranging (LiDAR) data, and GPS locations, to understand how vegetation and other attributes of seismic lines influence movements of two predators, wolves (Canis lupus) and grizzly bears (Ursus arctos). During winter, wolves moved towards seismic lines regardless of vegetation height, while during spring wolves moved towards seismic lines with higher vegetation. During summer, wolves moved towards seismic lines with lower vegetation and also moved faster near seismic lines with vegetation <0.7 m. Seismic lines with lower vegetation height were preferred by grizzly bears during spring and summer, but there was no relationship between vegetation height and grizzly bear movement rates. These results suggest that wolves use seismic lines for travel during summer, but during winter wolf movements relative to seismic lines could be influenced by factors additional to movement efficiency; potentially enhanced access to areas frequented by ungulate prey. Grizzly bears may be using seismic lines for movement, but could also be using seismic lines as a source of vegetative food or ungulate prey. To reduce wolf movement rate, restoration could focus on seismic lines with vegetation <1 m in height. However our results revealed that seismic lines continue to influence wolf movement behaviour decades after they were built, and even at later stages of regeneration. Therefore it remains unknown at what stage of natural regeneration, if any, wolves cease to respond to seismic lines. To reduce wolf response to seismic lines, active restoration tactics like blocking seismic lines and tree planting, along with management of alternate prey, could be evaluated. PMID:29659615

Incorporating induced seismicity in the 2014 United States National Seismic Hazard Model: results of the 2014 workshop and sensitivity studies

USGS Publications Warehouse

Petersen, Mark D.; Mueller, Charles S.; Moschetti, Morgan P.; Hoover, Susan M.; Rubinstein, Justin L.; Llenos, Andrea L.; Michael, Andrew J.; Ellsworth, William L.; McGarr, Arthur F.; Holland, Austin A.; Anderson, John G.

2015-01-01

The U.S. Geological Survey National Seismic Hazard Model for the conterminous United States was updated in 2014 to account for new methods, input models, and data necessary for assessing the seismic ground shaking hazard from natural (tectonic) earthquakes. The U.S. Geological Survey National Seismic Hazard Model project uses probabilistic seismic hazard analysis to quantify the rate of exceedance for earthquake ground shaking (ground motion). For the 2014 National Seismic Hazard Model assessment, the seismic hazard from potentially induced earthquakes was intentionally not considered because we had not determined how to properly treat these earthquakes for the seismic hazard analysis. The phrases “potentially induced” and “induced” are used interchangeably in this report, however it is acknowledged that this classification is based on circumstantial evidence and scientific judgment. For the 2014 National Seismic Hazard Model update, the potentially induced earthquakes were removed from the NSHM’s earthquake catalog, and the documentation states that we would consider alternative models for including induced seismicity in a future version of the National Seismic Hazard Model. As part of the process of incorporating induced seismicity into the seismic hazard model, we evaluate the sensitivity of the seismic hazard from induced seismicity to five parts of the hazard model: (1) the earthquake catalog, (2) earthquake rates, (3) earthquake locations, (4) earthquake Mmax (maximum magnitude), and (5) earthquake ground motions. We describe alternative input models for each of the five parts that represent differences in scientific opinions on induced seismicity characteristics. In this report, however, we do not weight these input models to come up with a preferred final model. Instead, we present a sensitivity study showing uniform seismic hazard maps obtained by applying the alternative input models for induced seismicity. The final model will be released after further consideration of the reliability and scientific acceptability of each alternative input model. Forecasting the seismic hazard from induced earthquakes is fundamentally different from forecasting the seismic hazard for natural, tectonic earthquakes. This is because the spatio-temporal patterns of induced earthquakes are reliant on economic forces and public policy decisions regarding extraction and injection of fluids. As such, the rates of induced earthquakes are inherently variable and nonstationary. Therefore, we only make maps based on an annual rate of exceedance rather than the 50-year rates calculated for previous U.S. Geological Survey hazard maps.

Hydra—The National Earthquake Information Center’s 24/7 seismic monitoring, analysis, catalog production, quality analysis, and special studies tool suite

USGS Publications Warehouse

Patton, John M.; Guy, Michelle R.; Benz, Harley M.; Buland, Raymond P.; Erickson, Brian K.; Kragness, David S.

2016-08-18

This report provides an overview of the capabilities and design of Hydra, the global seismic monitoring and analysis system used for earthquake response and catalog production at the U.S. Geological Survey National Earthquake Information Center (NEIC). Hydra supports the NEIC’s worldwide earthquake monitoring mission in areas such as seismic event detection, seismic data insertion and storage, seismic data processing and analysis, and seismic data output.The Hydra system automatically identifies seismic phase arrival times and detects the occurrence of earthquakes in near-real time. The system integrates and inserts parametric and waveform seismic data into discrete events in a database for analysis. Hydra computes seismic event parameters, including locations, multiple magnitudes, moment tensors, and depth estimates. Hydra supports the NEIC’s 24/7 analyst staff with a suite of seismic analysis graphical user interfaces.In addition to the NEIC’s monitoring needs, the system supports the processing of aftershock and temporary deployment data, and supports the NEIC’s quality assurance procedures. The Hydra system continues to be developed to expand its seismic analysis and monitoring capabilities.

Method of migrating seismic records

DOEpatents

Ober, Curtis C.; Romero, Louis A.; Ghiglia, Dennis C.

2000-01-01

The present invention provides a method of migrating seismic records that retains the information in the seismic records and allows migration with significant reductions in computing cost. The present invention comprises phase encoding seismic records and combining the encoded seismic records before migration. Phase encoding can minimize the effect of unwanted cross terms while still allowing significant reductions in the cost to migrate a number of seismic records.

Seismic instrumentation plan for the Hawaiian Volcano Observatory

USGS Publications Warehouse

Thelen, Weston A.

2014-01-01

The installation of new seismic stations is only the first part of building a volcanic early warning capability for seismicity in the State of Hawaii. Additional personnel will likely be required to study the volcanic processes at work under each volcano, analyze the current seismic activity at a level sufficient for early warning, build new tools for monitoring, maintain seismic computing resources, and maintain the new seismic stations.

Preliminary Analysis of Remote Triggered Seismicity in Northern Baja California Generated by the 2011, Tohoku-Oki, Japan Earthquake

NASA Astrophysics Data System (ADS)

Wong-Ortega, V.; Castro, R. R.; Gonzalez-Huizar, H.; Velasco, A. A.

2013-05-01

We analyze possible variations of seismicity in the northern Baja California due to the passage of seismic waves from the 2011, M9.0, Tohoku-Oki, Japan earthquake. The northwestern area of Baja California is characterized by a mountain range composed of crystalline rocks. These Peninsular Ranges of Baja California exhibits high microseismic activity and moderate size earthquakes. In the eastern region of Baja California shearing between the Pacific and the North American plates takes place and the Imperial and Cerro-Prieto faults generate most of the seismicity. The seismicity in these regions is monitored by the seismic network RESNOM operated by the Centro de Investigación Científica y de Educación Superior de Ensenada (CICESE). This network consists of 13 three-component seismic stations. We use the seismic catalog of RESNOM to search for changes in local seismic rates occurred after the passing of surface waves generated by the Tohoku-Oki, Japan earthquake. When we compare one month of seismicity before and after the M9.0 earthquake, the preliminary analysis shows absence of triggered seismicity in the northern Peninsular Ranges and an increase of seismicity south of the Mexicali valley where the Imperial fault jumps southwest and the Cerro Prieto fault continues.

Evaluation of induced seismicity forecast models in the Induced Seismicity Test Bench

NASA Astrophysics Data System (ADS)

Király, Eszter; Gischig, Valentin; Zechar, Jeremy; Doetsch, Joseph; Karvounis, Dimitrios; Wiemer, Stefan

2016-04-01

Induced earthquakes often accompany fluid injection, and the seismic hazard they pose threatens various underground engineering projects. Models to monitor and control induced seismic hazard with traffic light systems should be probabilistic, forward-looking, and updated as new data arrive. Here, we propose an Induced Seismicity Test Bench to test and rank such models. We apply the test bench to data from the Basel 2006 and Soultz-sous-Forêts 2004 geothermal stimulation projects, and we assess forecasts from two models that incorporate a different mix of physical understanding and stochastic representation of the induced sequences: Shapiro in Space (SiS) and Hydraulics and Seismics (HySei). SiS is based on three pillars: the seismicity rate is computed with help of the seismogenic index and a simple exponential decay of the seismicity; the magnitude distribution follows the Gutenberg-Richter relation; and seismicity is distributed in space based on smoothing seismicity during the learning period with 3D Gaussian kernels. The HySei model describes seismicity triggered by pressure diffusion with irreversible permeability enhancement. Our results show that neither model is fully superior to the other. HySei forecasts the seismicity rate well, but is only mediocre at forecasting the spatial distribution. On the other hand, SiS forecasts the spatial distribution well but not the seismicity rate. The shut-in phase is a difficult moment for both models in both reservoirs: the models tend to underpredict the seismicity rate around, and shortly after, shut-in. Ensemble models that combine HySei's rate forecast with SiS's spatial forecast outperform each individual model.

A decade of passive seismic monitoring experiments with local networks in four Italian regions

NASA Astrophysics Data System (ADS)

Chiaraluce, L.; Valoroso, L.; Anselmi, M.; Bagh, S.; Chiarabba, C.

2009-10-01

We report on four seismic monitoring experiments that in the past ten years we carried out with dense local networks in seismically active Italian areas where for at least a year, tens of three component seismic stations were set up to record microseismicity. The areas observed are Alpago-Cansiglio, located in the Venetian Alps, Città di Castello in the Northern Apennines, Marsica in the Central Apennines and Val d'Agri located in the Southern Apennines. We produced homogeneous catalogues regarding earthquake locations and local magnitudes to investigate seismicity patterns during an inter-seismic period. The four regions are characterised by different kinematics, strain rates and historical/recent seismicity. We investigate earthquake distribution in space, time and size obtaining reference seismic rates and parameters of the Gutenberg and Richter law. We declustered the catalogues to look for coherent signs in the background seismic activity. Despite a difference in the catalogues magnitudes of completeness due both to the diverse detection threshold of the local networks and different seismic release, we detect and observe two common main behaviours: a) The Alpago-Cansiglio and Marsica regions are characterised by a relatively lower rate of seismic release associated to the episodic occurrence of seismic sequences with the largest event being 3 < ML < 4. In these areas the seismicity is not localised around the main faults. b) The Città di Castello and Val d'Agri regions have a relatively high rate of seismicity release almost continuously with time, and the increase in earthquake production is not clearly related to seismic sequences. In these areas the seismicity nucleates around defined fault systems and is usually lower than ML < 3. We suggest that the presence of over-pressured fluids in the Città di Castello and Val d'Agri uppermost crustal volume may favour and mould the higher rate of microseismic release.

Mesoscale convective system surface pressure anomalies responsible for meteotsunamis along the U.S. East Coast on June 13th, 2013

PubMed Central

Wertman, Christina A.; Yablonsky, Richard M.; Shen, Yang; Merrill, John; Kincaid, Christopher R.; Pockalny, Robert A.

2014-01-01

Two destructive high-frequency sea level oscillation events occurred on June 13th, 2013 along the U.S. East Coast. Seafloor processes can be dismissed as the sources, as no concurrent offshore earthquakes or landslides were detected. Here, we present evidence that these tsunami-like events were generated by atmospheric mesoscale convective systems (MCSs) propagating from inland to offshore. The USArray Transportable Array inland and NOAA tide gauges along the coast recorded the pressure anomalies associated with the MCSs. Once offshore, the pressure anomalies generated shallow water waves, which were amplified by the resonance between the water column and atmospheric forcing. Analysis of the tidal data reveals that these waves reflected off the continental shelf break and reached the coast, where bathymetry and coastal geometry contributed to their hazard potential. This study demonstrates that monitoring MCS pressure anomalies in the interior of the U.S. provides important observations for early warnings of MCS-generated tsunamis. PMID:25420958

Active seismic experiment

NASA Technical Reports Server (NTRS)

Kovach, R. L.; Watkins, J. S.; Talwani, P.

1972-01-01

The Apollo 16 active seismic experiment (ASE) was designed to generate and monitor seismic waves for the study of the lunar near-surface structure. Several seismic energy sources are used: an astronaut-activated thumper device, a mortar package that contains rocket-launched grenades, and the impulse produced by the lunar module ascent. Analysis of some seismic signals recorded by the ASE has provided data concerning the near-surface structure at the Descartes landing site. Two compressional seismic velocities have so far been recognized in the seismic data. The deployment of the ASE is described, and the significant results obtained are discussed.

A frequency-domain seismic blind deconvolution based on Gini correlations

NASA Astrophysics Data System (ADS)

Wang, Zhiguo; Zhang, Bing; Gao, Jinghuai; Huo Liu, Qing

2018-02-01

In reflection seismic processing, the seismic blind deconvolution is a challenging problem, especially when the signal-to-noise ratio (SNR) of the seismic record is low and the length of the seismic record is short. As a solution to this ill-posed inverse problem, we assume that the reflectivity sequence is independent and identically distributed (i.i.d.). To infer the i.i.d. relationships from seismic data, we first introduce the Gini correlations (GCs) to construct a new criterion for the seismic blind deconvolution in the frequency-domain. Due to a unique feature, the GCs are robust in their higher tolerance of the low SNR data and less dependent on record length. Applications of the seismic blind deconvolution based on the GCs show their capacity in estimating the unknown seismic wavelet and the reflectivity sequence, whatever synthetic traces or field data, even with low SNR and short sample record.

DigiSeis—A software component for digitizing seismic signals using the PC sound card

NASA Astrophysics Data System (ADS)

Amin Khan, Khalid; Akhter, Gulraiz; Ahmad, Zulfiqar

2012-06-01

An innovative software-based approach to develop an inexpensive experimental seismic recorder is presented. This approach requires no hardware as the built-in PC sound card is used for digitization of seismic signals. DigiSeis, an ActiveX component is developed to capture the digitized seismic signals from the sound card and deliver them to applications for processing and display. A seismic recorder application software SeisWave is developed over this component, which provides real-time monitoring and display of seismic events picked by a pair of external geophones. This recorder can be used as an educational aid for conducting seismic experiments. It can also be connected with suitable seismic sensors to record earthquakes. The software application and the ActiveX component are available for download. This component can be used to develop seismic recording applications according to user specific requirements.

Seismic isolation of buildings using composite foundations based on metamaterials

NASA Astrophysics Data System (ADS)

Casablanca, O.; Ventura, G.; Garescı, F.; Azzerboni, B.; Chiaia, B.; Chiappini, M.; Finocchio, G.

2018-05-01

Metamaterials can be engineered to interact with waves in entirely new ways, finding application on the nanoscale in various fields such as optics and acoustics. In addition, acoustic metamaterials can be used in large-scale experiments for filtering and manipulating seismic waves (seismic metamaterials). Here, we propose seismic isolation based on a device that combines some properties of seismic metamaterials (e.g., periodic mass-in-mass systems) with that of a standard foundation positioned right below the building for isolation purposes. The concepts on which this solution is based are the local resonance and a dual-stiffness structure that preserves large (small) rigidity for compression (shear) effects. In other words, this paper introduces a different approach to seismic isolation by using certain principles of seismic metamaterials. The experimental demonstrator tested on the laboratory scale exhibits a spectral bandgap that begins at 4.5 Hz. Within the bandgap, it filters more than 50% of the seismic energy via an internal dissipation process. Our results open a path toward the seismic resilience of buildings and a critical infrastructure to shear seismic waves, achieving higher efficiency compared to traditional seismic insulators and passive energy-dissipation systems.

Illuminating Northern California’s Active Faults

USGS Publications Warehouse

Prentice, Carol S.; Crosby, Christopher J.; Whitehill, Caroline S.; Arrowsmith, J. Ramon; Furlong, Kevin P.; Philips, David A.

2009-01-01

Newly acquired light detection and ranging (lidar) topographic data provide a powerful community resource for the study of landforms associated with the plate boundary faults of northern California (Figure 1). In the spring of 2007, GeoEarthScope, a component of the EarthScope Facility construction project funded by the U.S. National Science Foundation, acquired approximately 2000 square kilometers of airborne lidar topographic data along major active fault zones of northern California. These data are now freely available in point cloud (x, y, z coordinate data for every laser return), digital elevation model (DEM), and KMZ (zipped Keyhole Markup Language, for use in Google EarthTM and other similar software) formats through the GEON OpenTopography Portal (http://www.OpenTopography.org/data). Importantly, vegetation can be digitally removed from lidar data, producing high-resolution images (0.5- or 1.0-meter DEMs) of the ground surface beneath forested regions that reveal landforms typically obscured by vegetation canopy (Figure 2)

Clinton Administration announces FY 2001 budget request

NASA Astrophysics Data System (ADS)

Showstack, Randy

Blessed with a strong US. economy the Clinton Administration on February 7 released a fiscal year 2001 federal budget request totaling a whopping $1,835 billion. Most of the funding request is slated for big ticket items including Social Security defense spending, Medicaid, Medicare, and paying down the federal debt. However, within the 19% of the budget that funds non-defense discretionary programs,science agencies receive fairly healthy increases.The National Science Foundation (NSF) budget request would increase NSF funding by 17.3% $675 million and bring the total budget request to $4.6 billion. This includes significant increases for several initiatives: biocomplexity in the environment, information technology research, nanoscale science and engineering, and 21st century workforce. Among the major Earth science projects are launching the Earthscope initiative which includes the US Array and San Andreas Fault Observatory at Depth (SAFOD) and the National Ecological Observatory Network (NEON).

Comparison of smoothing methods for the development of a smoothed seismicity model for Alaska and the implications for seismic hazard

NASA Astrophysics Data System (ADS)

Moschetti, M. P.; Mueller, C. S.; Boyd, O. S.; Petersen, M. D.

2013-12-01

In anticipation of the update of the Alaska seismic hazard maps (ASHMs) by the U. S. Geological Survey, we report progress on the comparison of smoothed seismicity models developed using fixed and adaptive smoothing algorithms, and investigate the sensitivity of seismic hazard to the models. While fault-based sources, such as those for great earthquakes in the Alaska-Aleutian subduction zone and for the ~10 shallow crustal faults within Alaska, dominate the seismic hazard estimates for locations near to the sources, smoothed seismicity rates make important contributions to seismic hazard away from fault-based sources and where knowledge of recurrence and magnitude is not sufficient for use in hazard studies. Recent developments in adaptive smoothing methods and statistical tests for evaluating and comparing rate models prompt us to investigate the appropriateness of adaptive smoothing for the ASHMs. We develop smoothed seismicity models for Alaska using fixed and adaptive smoothing methods and compare the resulting models by calculating and evaluating the joint likelihood test. We use the earthquake catalog, and associated completeness levels, developed for the 2007 ASHM to produce fixed-bandwidth-smoothed models with smoothing distances varying from 10 to 100 km and adaptively smoothed models. Adaptive smoothing follows the method of Helmstetter et al. and defines a unique smoothing distance for each earthquake epicenter from the distance to the nth nearest neighbor. The consequence of the adaptive smoothing methods is to reduce smoothing distances, causing locally increased seismicity rates, where seismicity rates are high and to increase smoothing distances where seismicity is sparse. We follow guidance from previous studies to optimize the neighbor number (n-value) by comparing model likelihood values, which estimate the likelihood that the observed earthquake epicenters from the recent catalog are derived from the smoothed rate models. We compare likelihood values from all rate models to rank the smoothing methods. We find that adaptively smoothed seismicity models yield better likelihood values than the fixed smoothing models. Holding all other (source and ground motion) models constant, we calculate seismic hazard curves for all points across Alaska on a 0.1 degree grid, using the adaptively smoothed and fixed smoothed seismicity models separately. Because adaptively smoothed models concentrate seismicity near the earthquake epicenters where seismicity rates are high, the corresponding hazard values are higher, locally, but reduced with distance from observed seismicity, relative to the hazard from fixed-bandwidth models. We suggest that adaptively smoothed seismicity models be considered for implementation in the update to the ASHMs because of their improved likelihood estimates relative to fixed smoothing methods; however, concomitant increases in seismic hazard will cause significant changes in regions of high seismicity, such as near the subduction zone, northeast of Kotzebue, and along the NNE trending zone of seismicity in the Alaskan interior.

Comparison of smoothing methods for the development of a smoothed seismicity model for Alaska and the implications for seismic hazard

USGS Publications Warehouse

Moschetti, Morgan P.; Mueller, Charles S.; Boyd, Oliver S.; Petersen, Mark D.

2014-01-01

In anticipation of the update of the Alaska seismic hazard maps (ASHMs) by the U. S. Geological Survey, we report progress on the comparison of smoothed seismicity models developed using fixed and adaptive smoothing algorithms, and investigate the sensitivity of seismic hazard to the models. While fault-based sources, such as those for great earthquakes in the Alaska-Aleutian subduction zone and for the ~10 shallow crustal faults within Alaska, dominate the seismic hazard estimates for locations near to the sources, smoothed seismicity rates make important contributions to seismic hazard away from fault-based sources and where knowledge of recurrence and magnitude is not sufficient for use in hazard studies. Recent developments in adaptive smoothing methods and statistical tests for evaluating and comparing rate models prompt us to investigate the appropriateness of adaptive smoothing for the ASHMs. We develop smoothed seismicity models for Alaska using fixed and adaptive smoothing methods and compare the resulting models by calculating and evaluating the joint likelihood test. We use the earthquake catalog, and associated completeness levels, developed for the 2007 ASHM to produce fixed-bandwidth-smoothed models with smoothing distances varying from 10 to 100 km and adaptively smoothed models. Adaptive smoothing follows the method of Helmstetter et al. and defines a unique smoothing distance for each earthquake epicenter from the distance to the nth nearest neighbor. The consequence of the adaptive smoothing methods is to reduce smoothing distances, causing locally increased seismicity rates, where seismicity rates are high and to increase smoothing distances where seismicity is sparse. We follow guidance from previous studies to optimize the neighbor number (n-value) by comparing model likelihood values, which estimate the likelihood that the observed earthquake epicenters from the recent catalog are derived from the smoothed rate models. We compare likelihood values from all rate models to rank the smoothing methods. We find that adaptively smoothed seismicity models yield better likelihood values than the fixed smoothing models. Holding all other (source and ground motion) models constant, we calculate seismic hazard curves for all points across Alaska on a 0.1 degree grid, using the adaptively smoothed and fixed smoothed seismicity models separately. Because adaptively smoothed models concentrate seismicity near the earthquake epicenters where seismicity rates are high, the corresponding hazard values are higher, locally, but reduced with distance from observed seismicity, relative to the hazard from fixed-bandwidth models. We suggest that adaptively smoothed seismicity models be considered for implementation in the update to the ASHMs because of their improved likelihood estimates relative to fixed smoothing methods; however, concomitant increases in seismic hazard will cause significant changes in regions of high seismicity, such as near the subduction zone, northeast of Kotzebue, and along the NNE trending zone of seismicity in the Alaskan interior.

The influence of the mining operation on the mine seismicity of Vorkuta coal deposit

NASA Astrophysics Data System (ADS)

Zmushko, T.; Turuntaev, S. B.; Kulikov, V. I.

2012-04-01

The mine seismicity of Vorkuta coal deposit was analyzed. Seismic network consisting of 24 seismic sensors (accelerometers) cover the area of "Komsomolskaya" and "North" mines of Vorkuta deposit. Also there is seismic station of IDG RAS with three-component seismometer near this mines for better defining energy of the seismic events. The catalogs of seismic events contain 9000 and 7000 events with maximum magnitude M=2.3 for "Komsomolskaya" and "North" mines respectively and include the period from 01.09.2008 to 01.09.2011. The b-value of the magnitude-frequency relation was -1.0 and -1.15 respectively for the mines, meanwhile b-value for the nature seismicity was -0,9. It was found, that the number of seismic events per hour during mine combine operation is higher in 2.5 times than the number of seismic events during the break in the operation. Also, the total energy of the events per hour during the operation is higher in 3-5 times than during the break. The study showed, that the number and the energy of the seismic events relate with the hours of mine combine operation. The spatial distribution of the seismic events showed, that 80% of all events and 85% of strong events (M>1.6) were located in and near the longwall under development during the mine combine operations as well asduring the breaks. The isoclines of seismic event numbers proved that the direction of motion of the boundary of seismic events extension coincides with the direction of development, the maximum number of events for any period lies within the wall under operation. The rockburst with M=2.3 occurring at the North mine at July 16, 2011 was considered. The dependences of the energy and of the number of events with different magnitudes on the time showed that the number of events with M=1 and especially M=0.5 before the rockburst decreased, which corresponds to the prognostic seismic quietness, described in the research works. The spatial distribution of the events for the 6 month before the rockburst showed that the rockbust occurred at some distance from the main group of seismic events, in an area where the vent brake slope was made at that time. It was found that there is an area where the coal was not developed, but the seismic events occured. Such area could be noticed before the moment of the rockburst. The spatial distribution of the seismic events during the "seismic quietness" showed that for events with M = 1, and especially for the events with M = 0.5, the analogue of "seismic gap" (the area without events between the seismically active areas) can be noticed. The rockburst occurred at the boundary of the "seismic gap". Obtained results (which are in correspondence with known natural earthquake prediction phenomena) could be used for forecast of the considered rockburst in a 1 month before it occurred.

Emergency seismic and CGPS networks: a first employment for the L'Aquila Mw 6.3 earthquake

NASA Astrophysics Data System (ADS)

Abruzzese, L.; Avallone, A.; Cecere, G.; Cattaneo, M.; Cardinale, V.; Castagnozzi, A.; Cogliano, R.; Criscuoli, F.; D'Agostino, N.; D'Ambrosio, C.; de Luca, G.; D'Anastasio, E.; Falco, L.; Flammia, V.; Migliari, F.; Minichiello, F.; Memmolo, A.; Monachesi, G.; Moschillo, R.; Pignone, M.; Pucillo, S.; Selvaggi, G.; Zarrilli, L.; Delladio, A.; Govoni, A.; Franceschi, D.; de Martin, M.; Moretti, M.

2009-12-01

During the last 2 years, the Istituto Nazionale di Geofisica e Vulcanologia (INGV) developed an important real-time temporary seismic network infrastructure in order to densify the Italian National Seismic Network in epicentral areas thus enhancing the localization of the micro-seismicity after main earthquake events. This real-time temporary seismic network is constituted by various mobile and autonomous seismic stations that in group of three are telemetered to a Very Small Aperture Terminal (VSAT). This system uses a dedicated bandwidth on UHF, Wi-Fi and satellite frequency that allows the data flow in real-time at INGV centre in Rome (and Grottaminarda as backup center). The deployment of the seismic network is managed in a geographical information systems (GIS) by particular scenarios that visualizes, for the epicentral area, information about instrumental seismicity, seismic risk, macroseismic felts and territorial data. Starting from digital terrain model, the surface spatial analysis (Viewshed, Observer Point) allows the geographic arrangement of the stations and relative scenarios. The April, 6th, 2009 Mw 6.3 L'Aquila destructive earthquake represented the first real-case to test the entire emergency seismic network infrastructure. Less than 6 hours after the earthquake occurrence, a first accelerometer station was already sending data at INGV seismic monitoring headquarters. A total number of 9 seismic stations have been installed within 3 days after the earthquake. Furthermore, 5 permanent GPS stations have been installed in the epicentral area within 1 to 9 days after the main shock to detect the post-seismic deformation induced by the earthquake. We will show and describe the details of the Emergency Seismic Network infrastructure, and the first results from the collected data.

New comprehensive standard seismic noise models and 3D seismic noise variation for Morocco territory, North Africa, obtained using seismic broadband stations

NASA Astrophysics Data System (ADS)

El Fellah, Younes; El-Aal, Abd El-Aziz Khairy Abd; Harnafi, Mimoun; Villaseñor, Antonio

2017-05-01

In the current work, we constructed new comprehensive standard seismic noise models and 3D temporal-spatial seismic noise level cubes for Morocco in north-west Africa to be used for seismological and engineering purposes. Indeed, the original global standard seismic noise models published by Peterson (1993) and their following updates by Astiz and Creager (1995), Ekström (2001) and Berger et al. (2003) had no contributing seismic stations deployed in North Africa. Consequently, this preliminary study was conducted to shed light on seismic noise levels specific to north-west Africa. For this purpose, 23 broadband seismic stations recently installed in different structural domains throughout Morocco are used to study the nature and characteristics of seismic noise and to create seismic noise models for Morocco. Continuous data recorded during 2009, 2010 and 2011 were processed and analysed to construct these new noise models and 3D noise levels from all stations. We compared the Peterson new high-noise model (NHNM) and low-noise model (NLNM) with the Moroccan high-noise model (MHNM) and low-noise model (MLNM). These new noise models are comparable to the United States Geological Survey (USGS) models in the short period band; however, in the period range 1.2 s to 1000 s for MLNM and 10 s to 1000 s for MHNM display significant variations. This variation is attributed to differences in the nature of seismic noise sources that dominate Morocco in these period bands. The results of this study have a new perception about permanent seismic noise models for this spectacular region and can be considered a significant contribution because it supplements the Peterson models and can also be used to site future permanent seismic stations in Morocco.

Estimating Local and Near-Regional Velocity and Attenuation Structure from Seismic Noise

DTIC Science & Technology

2008-09-30

seismic array in Costa Rica and Nicaragua from ambient seismic noise using two independent methods, noise cross correlation and beamforming. The noise...Mean-phase velocity-dispersion curves are calculated for the TUCAN seismic array in Costa Rica and Nicaragua from ambient seismic noise using two...stations of the TUCAN seismic array (Figure 4c) using a method similar to Harmon et al. (2007). Variations from Harmon et al. (2007) include removing the

Recent Seismicity in Texas and Research Design and Progress of the TexNet-CISR Collaboration

NASA Astrophysics Data System (ADS)

Hennings, P.; Savvaidis, A.; Rathje, E.; Olson, J. E.; DeShon, H. R.; Datta-Gupta, A.; Eichhubl, P.; Nicot, J. P.; Kahlor, L. A.

2017-12-01

The recent increase in the rate of seismicity in Texas has prompted the establishment of an interdisciplinary, interinstitutional collaboration led by the Texas Bureau of Economic Geology which includes the TexNet Seismic Monitoring and Research project as funded by The State of Texas (roughly 2/3rds of our funding) and the industry-funded Center for Integrated Seismicity Research (CISR) (1/3 of funding). TexNet is monitoring and cataloging seismicity across Texas using a new backbone seismic network, investigating site-specific earthquake sequences by deploying temporary seismic monitoring stations, and conducting reservoir modeling studies. CISR expands TexNet research into the interdisciplinary realm to more thoroughly study the factors that contribute to seismicity, characterize the associated hazard and risk, develop strategies for mitigation and management, and develop methods of effective communication for all stakeholders. The TexNet-CISR research portfolio has 6 themes: seismicity monitoring, seismology, geologic and hydrologic description, geomechanics and reservoir modeling, seismic hazard and risk assessment, and seismic risk social science. Twenty+ specific research projects span and connect these themes. We will provide a synopsis of research progress including recent seismicity trends in Texas; Fort Worth Basin integrated studies including geological modeling and fault characterization, fluid injection data syntheses, and reservoir and geomechanical modeling; regional ground shaking characterization and mapping, infrastructure vulnerability assessment; and social science topics of public perception and information seeking behavior.

78 FR 59732 - Revisions to Design of Structures, Components, Equipment, and Systems

Federal Register 2010, 2011, 2012, 2013, 2014

2013-09-27

...,'' Section 3.7.2, ``Seismic System Analysis,'' Section 3.7.3, ``Seismic Subsystem Analysis,'' Section 3.8.1... Analysis,'' (Accession No. ML13198A223); Section 3.7.3, ``Seismic Subsystem Analysis,'' (Accession No..., ``Seismic System Analysis,'' Section 3.7.3, ``Seismic Subsystem Analysis,'' Section 3.8.1, ``Concrete...

Probing the internal structure of the asteriod Didymoon with a passive seismic investigation

NASA Astrophysics Data System (ADS)

Murdoch, N.; Hempel, S.; Pou, L.; Cadu, A.; Garcia, R. F.; Mimoun, D.; Margerin, L.; Karatekin, O.

2017-09-01

Understanding the internal structure of an asteroid has important implications for interpreting its evolutionary history, for understanding its continuing geological evolution, and also for asteroid deflection and in-situ space resource utilisation. Given the strong evidence that asteroids are seismically active, an in-situ passive seismic experiment could provide information about the asteroid surface and interior properties. Here, we discuss the natural seismic activity that may be present on Didymoon, the secondary component of asteroid (65803) Didymos. Our analysis of the tidal stresses in Didymoon shows that tidal quakes are likely to occur if the secondary has an eccentric orbit. Failure occurs most easily at the asteroid poles and close to the surface for both homogeneous and layered internal structures. Simulations of seismic wave propagation in Didymoon show that the seismic moment of even small meteoroid impacts can generate clearly observable body and surface waves if the asteroid's internal structure is homogeneous. The presence of a regolith layer over a consolidated core can result in the seismic energy becoming trapped in the regolith due to the strong impedance contrast at the regolith-core boundary. The inclusion of macro-porosity (voids) further complexifies the wavefield due to increased scattering. The most prominent seismic waves are always found to be those traveling along the surface of the asteroid and those focusing in the antipodal point of the seismic source. We find also that the waveforms and ground acceleration spectra allow discrimination between the different internal structure models. Although the science return of a passive seismic experiment would be enhanced by having multiple seismic stations, one single seismic station can already vastly improve our knowledge about the seismic environment and sub-surface structure of an asteroid. We describe several seismic measurement techniques that could be applied in order to study the asteroid internal structure with one three-component seismic station.

Evaluation of the Seismic Hazard in Venezuela with a revised seismic catalog that seeks for harmonization along the country borders

NASA Astrophysics Data System (ADS)

Rendon, H.; Alvarado, L.; Paolini, M.; Olbrich, F.; González, J.; Ascanio, W.

2013-05-01

Probabilistic Seismic Hazard Assessment is a complex endeavor that relies on the quality of the information that comes from different sources: the seismic catalog, active faults parameters, strain rates, etc. Having this in mind, during the last several months, the FUNVISIS seismic hazard group has been working on a review and update of the local data base that form the basis for a reliable PSHA calculation. In particular, the seismic catalog, which provides the necessary information that allows the evaluation of the critical b-value, which controls how seismic occurrence distributes with magnitude, has received particular attention. The seismic catalog is the result of the effort of several generations of researchers along the years; therefore, the catalog necessarily suffers from the lack of consistency, homogeneity and completeness for all ranges of magnitude over any seismic study area. Merging the FUNVISIS instrumental catalog with the ones obtained from international agencies, we present the work that we have been doing to produce a consistent seismic catalog that covers Venezuela entirely, with seismic events starting from 1910 until 2012, and report the magnitude of completeness for the different periods. Also, we present preliminary results on the Seismic Hazard evaluation that takes into account such instrumental catalog, the historical catalog, updated known fault geometries and its correspondent parameters, and the new seismic sources that have been defined accordingly. Within the spirit of the Global Earthquake Model (GEM), all these efforts look for possible bridges with neighboring countries to establish consistent hazard maps across the borders.

Temporal Delineation and Quantification of Short Term Clustered Mining Seismicity

NASA Astrophysics Data System (ADS)

Woodward, Kyle; Wesseloo, Johan; Potvin, Yves

2017-07-01

The assessment of the temporal characteristics of seismicity is fundamental to understanding and quantifying the seismic hazard associated with mining, the effectiveness of strategies and tactics used to manage seismic hazard, and the relationship between seismicity and changes to the mining environment. This article aims to improve the accuracy and precision in which the temporal dimension of seismic responses can be quantified and delineated. We present a review and discussion on the occurrence of time-dependent mining seismicity with a specific focus on temporal modelling and the modified Omori law (MOL). This forms the basis for the development of a simple weighted metric that allows for the consistent temporal delineation and quantification of a seismic response. The optimisation of this metric allows for the selection of the most appropriate modelling interval given the temporal attributes of time-dependent mining seismicity. We evaluate the performance weighted metric for the modelling of a synthetic seismic dataset. This assessment shows that seismic responses can be quantified and delineated by the MOL, with reasonable accuracy and precision, when the modelling is optimised by evaluating the weighted MLE metric. Furthermore, this assessment highlights that decreased weighted MLE metric performance can be expected if there is a lack of contrast between the temporal characteristics of events associated with different processes.

Improved earthquake monitoring in the central and eastern United States in support of seismic assessments for critical facilities

USGS Publications Warehouse

Leith, William S.; Benz, Harley M.; Herrmann, Robert B.

2011-01-01

Evaluation of seismic monitoring capabilities in the central and eastern United States for critical facilities - including nuclear powerplants - focused on specific improvements to understand better the seismic hazards in the region. The report is not an assessment of seismic safety at nuclear plants. To accomplish the evaluation and to provide suggestions for improvements using funding from the American Recovery and Reinvestment Act of 2009, the U.S. Geological Survey examined addition of new strong-motion seismic stations in areas of seismic activity and addition of new seismic stations near nuclear power-plant locations, along with integration of data from the Transportable Array of some 400 mobile seismic stations. Some 38 and 68 stations, respectively, were suggested for addition in active seismic zones and near-power-plant locations. Expansion of databases for strong-motion and other earthquake source-characterization data also was evaluated. Recognizing pragmatic limitations of station deployment, augmentation of existing deployments provides improvements in source characterization by quantification of near-source attenuation in regions where larger earthquakes are expected. That augmentation also supports systematic data collection from existing networks. The report further utilizes the application of modeling procedures and processing algorithms, with the additional stations and the improved seismic databases, to leverage the capabilities of existing and expanded seismic arrays.

A first step to compare geodynamical models and seismic observations of the inner core

NASA Astrophysics Data System (ADS)

Lasbleis, M.; Waszek, L.; Day, E. A.

2016-12-01

Seismic observations have revealed a complex inner core, with lateral and radial heterogeneities at all observable scales. The dominant feature is the east-west hemispherical dichotomy in seismic velocity and attenuation. Several geodynamical models have been proposed to explain the observed structure: convective instabilities, external forces, crystallisation processes or influence of outer core convection. However, interpreting such geodynamical models in terms of the seismic observations is difficult, and has been performed only for very specific models (Geballe 2013, Lincot 2014, 2016). Here, we propose a common framework to make such comparisons. We have developed a Python code that propagates seismic ray paths through kinematic geodynamical models for the inner core, computing a synthetic seismic data set that can be compared to seismic observations. Following the method of Geballe 2013, we start with the simple model of translation. For this, the seismic velocity is proposed to be function of the age or initial growth rate of the material (since there is no deformation included in our models); the assumption is reasonable when considering translation, growth and super rotation of the inner core. Using both artificial (random) seismic ray data sets and a real inner core data set (from Waszek et al. 2011), we compare these different models. Our goal is to determine the model which best matches the seismic observations. Preliminary results show that super rotation successfully creates an eastward shift in properties with depth, as has been observed seismically. Neither the growth rate of inner core material nor the relationship between crystal size and seismic velocity are well constrained. Consequently our method does not directly compute the seismic travel times. Instead, here we use age, growth rate and other parameters as proxies for the seismic properties, which represent a good first step to compare geodynamical and seismic observations.Ultimately we aim to release our codes to broader scientific community, allowing researchers from all disciplines to test their models of inner core growth against seismic observations or create a kinematic model for the evolution of the inner core which matches new geophysical observations.